THE PSYCHOLOGY OF PERSECUTORY freeman2007.pdf

Clinical Psychology Review 27 (2007) 425 – 457

Suspicious minds: The psychology of persecutory delusions Daniel Freeman Department of Psychology, PO Box 77, Institute of Psychiatry, King’s College London, Denmark Hill, London, SE5 8AF, UK Received 6 July 2006; accepted 10 October 2006

Abstract At least 10–15% of the general population regularly experience paranoid thoughts and persecutory delusions are a frequent symptom of psychosis. Persecutory ideation is a key topic for study. In this article the empirical literature on psychological processes associated with persecutory thinking in clinical and non-clinical populations is comprehensively reviewed. There is a large direct affective contribution to the experience. In particular, anxiety affects the content, distress and persistence of paranoia. In the majority of cases paranoia does not serve a defensive function, but instead builds on interpersonal concerns conscious to the person. However, affect alone is not sufficient to produce paranoid experiences. There is also evidence that anomalous internal experiences may be important in leading to odd thought content and that a jumping to conclusions reasoning bias is present in individuals with persecutory delusions. Theory of mind functioning has received particular research attention recently but the findings do not support a specific association with paranoia. The threat anticipation cognitive model of persecutory delusions is presented, in which persecutory delusions are hypothesised to arise from an interaction of emotional processes, anomalous experiences and reasoning biases. Ten key future research questions are identified, including the need for researchers to consider factors important to the different dimensions of delusional experience. © 2006 Elsevier Ltd. All rights reserved. Keywords: Delusions; Paranoia; Cognitive; Schizophrenia; Psychosis

1. Introduction We are living in paranoid times, with fears of others attaining a new intensity. Nonetheless, being overly wary of the intentions of others has long been recognised as a problem. In the seventeenth century Francis Bacon (1612), often credited as the founder of the scientific method, commented on the corrosive nature of the experience: ‘Suspicions amongst thoughts are like bats amongst birds, — they ever fly by twilight. Certainly they are to be repressed, or, at the least, well guarded. For they cloud the mind, they lose friends, and they check with business, whereby business cannot go on currently and constantly. They dispose kings to tyranny, husbands to jealousy, wise men to irresolution and melancholy.’ Yet in the last 10 years there has been a rapid development in the understanding of persecutory thinking, assisted by the focus on it as a phenomenon of interest in its own right rather than simply as a symptom of severe mental illness (Bentall, 1990). The argument that will be put forward in this review is that there is now an excellent opportunity to E-mail address: [email protected]. 0272-7358/$ - see front matter © 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.cpr.2006.10.004

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take the starting point of this work of the last 10 years and make dramatic increases in the understanding of persecutory thinking. Explanatory models can become as powerful as those for emotional disorders and lead to more effective psychological interventions for paranoia. But also emphasised are the significant conceptual and methodological limitations of previous work. 2. The definition of persecutory delusions There have, of course, been many commentaries on the limitations of definitions of delusional beliefs in general, in that most criteria do not apply to all delusions, which partly results from epistemological difficulties in determining the referent of a name by a single set of necessary or sufficient characteristics (see Kripke, 1980). This has all too often been a rarefied academic debate without consideration of the implications for research or clinical practice. The most sustainable position is that of Oltmanns (1988). Assessing the presence of a delusion may best be accomplished by considering a list of characteristics or dimensions, none of which is necessary or sufficient, that with increasing endorsement produces greater agreement on the presence of a delusion. For instance, the more a belief is implausible, unfounded, strongly held, not shared by others, distressing and preoccupying then the more likely it is to be considered a delusion. The practical importance of the debate about defining delusions is that it informs us that there is individual variability in the characteristics of delusional experience (see Table 1). Delusions are definitely not discrete discontinuous entities. They are complex, multi-dimensional phenomena (Garety & Hemsley, 1994). The implication is that there can be no simple answer to the question ‘What causes a delusion?’ Instead, an understanding of each dimension of delusional experience is needed: what causes the content of a delusion? What causes the degree of belief conviction? What causes resistance to change? What causes the distress? It is plausible that different factors are involved in different dimensions of delusional experience. Research on the causes of different dimensions of delusional experience is rare; a few studies consider delusional conviction (Freeman et al., 2004; Garety et al., 2005) and delusional distress (Freeman & Garety, 1999; Freeman, Garety, & Kuipers, 2001; Startup, Freeman, & Garety, in press). The implication for clinical practice is that clinicians need to think with clients about the aspect of delusional experience they are hoping will change during the course of an intervention (see Birchwood & Trower, 2006) and formulate accordingly. In contrast to the debates about defining delusions, diagnostic criteria for sub-types of delusional beliefs based upon content have not been a topic of comment. Many reports of studies are unclear about the definition of persecutory delusions used. This is perhaps because the issue is thought to be self-evident, but it is more complex than might be Table 1 The multi-dimensional nature of delusions Characteristic of delusions

Variability in characteristic

Unfounded

For some individuals the delusions reflect a kernel of truth that has been exaggerated (e.g. the person had a dispute with the neighbour but now believes that the whole neighbourhood is monitoring them and will harm them). It can be difficult to determine whether the person is actually delusional. For others the ideas are fantastic, impossible and clearly unfounded (e.g. the person believes that s/he was present at the time of the Big Bang and is involved in battles across the universe and heavens). Beliefs can vary from being held with 100% conviction to only occasionally being believed when the person is in a particular stressful situation. An individual may be certain that they could not be mistaken and will not countenance any alternative explanation for their experiences. Others feel very confused and uncertain about their ideas and readily want to think about alternative accounts of their experiences. Some people report that they can do nothing but think about their delusional concerns. For other people, although they firmly believe the delusion, such thoughts rarely come into their mind. Many beliefs, especially those seen in clinical practice, are very distressing (e.g. persecutory delusions) but others (e.g. grandiose delusions) can actually be experienced positively. Even some persecutory delusions can be associated with low levels of distress (e.g. the individual believes that the persecutor hasn't the power to harm them). Delusions can stop people interacting with others and lead to great isolation and abandonment of activities. Other people can have a delusion and still function at a high level including maintaining relationships and employment. In many instances the patient is at the centre of the delusional system (e.g. ‘I have been singled out for persecution’). However friends and relatives can be involved (e.g. ‘They are targeting my whole family’) and some people believe that everybody is affected equally (e.g. ‘Everybody is being experimented upon’).

Firmly held Resistant to change

Preoccupying Distressing

Interferes with social functioning Involves personal reference

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Table 2 Criteria for a delusion to be classified as persecutory (Freeman & Garety, 2000) Criteria A and B must be met: A. The individual believes that harm is occurring, or is going to occur, to him or her. B. The individual believes that the persecutor has the intention to cause harm. There are a number of points of clarification: Harm concerns any action that leads to the individual experiencing distress. Harm only to friends or relatives does not count as a persecutory belief, unless the persecutor also intends this to have a negative effect upon the individual. The individual must believe that the persecutor at present or in the future will attempt to harm him or her. Delusions of reference do not count within the category of persecutory beliefs.

considered at first sight. There is great variety in the content of persecutory thoughts, for instance, in the type and timing of threat, the target of the harm, and the identity and intention of the persecutor (Freeman et al., 2001). Furthermore, terms such as paranoia, delusions of persecution, and delusions of reference have been used interchangeably and to refer to different concepts. Freeman and Garety (2000) clarify the definition of persecutory ideation: the individual believes that harm is occurring, or is going to occur, to him or her, and that the persecutor has the intention to cause harm (see Table 2). The second element of the definition distinguishes persecutory from anxious thoughts. Use of clear criteria such as these, coupled with descriptions of the levels of conviction and distress in participant groups, will enable both a focus on pure phenomena and comparisons across research studies. 3. The epidemiology of paranoid thinking Surprisingly, the epidemiology of persecutory ideation has not been systematically reviewed. Basic information on the prevalence and distribution of paranoid thoughts is key in determining the importance of the experience and the most appropriate research strategy. This neglected area will therefore be given some consideration. Persecutory delusions, as most people are aware, are taken as a key sign of severe mental illnesses such as schizophrenia. Sartorius et al. (1986) present findings from a World Health Organisation prospective study in ten countries of individuals with signs of schizophrenia making first contact with services (N = 1379). Persecutory delusions were the second most common symptom of psychosis, after delusions of reference, occurring in almost 50% of cases. However, there are many other diagnoses in which persecutory delusions occur in a substantial minority. The presence of delusions and hallucinations in unipolar depression is approximately 15% (Johnson, Horwath, & Weissman, 1991). Again, persecutory beliefs are a common presentation of these delusions: a case-note review by Frangos, Athanassenas, Tsitourides, Psilolignos, and Katsanou (1983) found that 44% of patients with unipolar depressive psychosis (N = 136) had persecutory delusions. In a review of bipolar disorder, Goodwin and Jamison (1990) suggest that persecutory delusions (28%) are frequent in manic episodes. There is evidence from small-scale clinical studies that psychotic symptoms occur in approximately 30% of cases of combat-related PTSD (Butler, Mueser, Sprock, & Braff, 1996; Hamner, Freuch, Ulmer, & Arana, 1999). Hallucinations are the most common psychotic symptom associated with PTSD, but delusions also occur, particularly with a persecutory theme. Persecutory ideation is of course likely to be common in paranoid personality disorder, the main criterion for which is that the person has ‘a pervasive distrust and suspiciousness of others such that their motives are interpreted as malevolent’ (DSM-IV; APA, 1994). It is also of note that people with anxiety or depression have elevated scores on measures of persecutory ideation (Van Os et al., 1999). Finally, persecutory delusions occur in neurological disorders, such as dementia (Flint, 1991) and epilepsy (Trimble, 1992). For instance, Rubin, Drevets, and Burke (1988) report that 31% of 110 individuals with dementia of the Alzheimer type had paranoid delusions. Many have argued that psychotic symptoms such as delusions might be better understood on a continuum with normal experience (Chapman & Chapman, 1980; Claridge, 1997; Johns, 2005; Peters, Joseph, & Garety, 1999; Van Os & Verdoux, 2003; Strauss, 1969). Delusions in psychosis would represent the severe end of a continuum, but such experiences would be present, often to a lesser degree, in the general population, and this would be related to milder attenuated forms of the experience. For example, a clinical persecutory delusion about government attempts to kill the person would be considered related to non-clinical delusions about neighbours trying to get at the person that would in turn be considered as related to everyday suspicions about the intentions of others. However, it should be emphasised that there are different forms of the continuum view (Claridge, 1994) and the distribution of symptoms may well be

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Table 3 Studies of paranoid thinking in non-clinical populations Study

N

Representative general population studies Epidemiologic 810 adults in Baltimore, Catchment Area United States (weighted (EPA) program for larger population of Eaton et al. (1991) 3481 from which this sub-sample was drawn)

Epidemiologic Catchment Area (EPA) program prospective study Tien and Anthony 4994 adults (aged 18 to (1990) 49 years) were selected from the US survey who had not reported any psychotic symptoms at the baseline assessment. They were then assessed 1 year later.

2000 British National Survey of Psychiatric Morbidity Johns et al. (2004)

8580 adults in the United Kingdom (aged 16–74) (60 individuals with psychosis were then excluded)

Assessment

Time period Prevalence

Diagnostic Interview Schedule (Robins et al., 1981). This schedule was not administered by a mental health professional.

Past month

Symptom endorsement is reported first followed by clinical symptom level in brackets People spying on you 12% (1%) People following you 8% (1%) Trying to hurt you 5% (1%) Reading your mind 2% (1%) Others control you 2% (2%) Steal thoughts 2% (1%)

Diagnostic Interview Schedule (Robins et al., 1981). This schedule was not administered by a mental health professional.

New occurrence of symptoms in the past year.

Psychosis Screening Questionnaire (Bebbington & Nayani, 1995). Not administered by mental health professional.

Past year

New symptom onset: Believed people were watching you or spying on you? 2.6% Believed people were following you? 1.6% Believed someone was plotting against you or trying to hurt you or poison you? 0.5% Believed someone was reading your mind? 0.6% Believed others were controlling how you moved or what you thought against your will? 0.3% Felt that someone or something could put strange thoughts directly into your mind of could take or steal thoughts out of your mind? 0.2% Paranoia Over the past year, have there been times when you felt that people were against you? 21.2% Have there been times when you felt that people were deliberately acting to harm you or your interests? 9.1% Have there been times when you felt that a group of people were plotting to cause you serious harm or injury? 1.5% Thought insertion Over the past year, have you ever felt that your thoughts were directly interfered with or controlled by some outside force or person? 9.0% Did this come about in a way that many people would find hard to believe, for instance, through telepathy? 0.9%

Representative older adult general population studies Older American 997 adults (aged 65+) Mini-Mult Resources and in Durham County, (Kincannon, 1968) Services (OARS) — N.C., USA Durham survey Christenson and Blazer (1984) Kungsholmen project 1420 adults (aged 75+) Comprehensive Forsell and in Stockholm, Sweden. Psychopathological Rating Henderson (1998) People living in all types Scale (CPRS) (Äsberg et al., of institutions were also 1978). Assessment by mental included. health professional.

For total group ‘generalised persecutory ideation’ 4% For group without cognitive impairment (N = 781) ‘Generalised persecutory ideation’ 2% 6.3% had paranoid symptom. For individuals without cognitive impairment the prevalence was 2.6%

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Table 3 (continued ) Study

N

Assessment

Time period Prevalence

Representative older adult general population studies Last Longitudinal 347 adults (aged 85) Comprehensive month Psychopathological Rating Gerontological and without dementia Geriatric Population representative of a Scale (Äsberg et al., birth cohort in Göteborg, 1978). Administered Study Östling and Skoog (2002) Sweden. by a mental health professional. Plus informant interview and inspection of medical records. King's County, 1027 adults (aged 55+) Paranoid sub-scale of the Past week Brooklyn study. without cognitive SCL-90 (Derogatis, Lipman, Cohen et al. (2004) impairment in Brooklyn, & Covi, 1973). N.Y., USA. Four ethnic Self-report questionnaire. groups sampled.

Studies of selected non-clinical samples Columbia University 1005 adults (aged Study Olfson et al. 18–70) attending (2002) a general medicine practice in northern Manhattan, N.Y., USA.

Aquitaine Sentinel Network study Verdoux et al. (1998)

Paranoia survey Freeman, Garety, Bebbington, Smith et al. (2005)

462 adults (18+ years) without psychiatric disorder attending general medicine practices in Southwest France 1202 university students (ages 16–61) in Southeast England, UK

Mini International Neuropsychiatric Interview (Sheehan et al., 1998). Not administered by a mental health professional.

Currently present

Peters et al. Delusions Inventory (PDI) (Peters et al., 1999). Self-report questionnaire.

Lifetime

Paranoia Checklist. Self-report questionnaire.

Last month

Belief of being persecuted, harassed, or unfairly treated that did not reach delusional proportions was classified as paranoid ideation 6.9% Persecutory delusion 3.5%

Paranoid ideation present in 13% Paranoid ideation was considered present if the respondent endorsed three or more items. The items in the scale are: Feeling that you are watched or talked about by others. Having ideas or beliefs that others do not share Others not giving you proper credit for your achievements Feeling that people will take advantage of you if you let them Feeling others are to blame for most of your troubles Feeling that most people cannot be trusted

Belief that others were spying on or following them 10.6% Belief that people were plotting or trying to poison them 6.9% Delusion of reference 4.7% Belief that people were secretly testing or experimenting on them 4.6% Do you ever feel as if you are being persecuted in some way? 25.5% Do you ever feel there is a conspiracy against you? 10.4%

Percentages of sample experiencing paranoid thoughts at least weekly: There might be negative comments being circulated about me 42% Bad things are being said about me behind my back 30% People deliberately try to irritate me 27% I might be being observed or followed 19% People are trying to make me upset 12% Someone I know has bad intentions towards me 12% I am under threat from others 10% I have a suspicion that someone has it in for me 8% Someone I don't know has bad intentions towards me 8% People would harm me if given the opportunity 8% There is a possibility of a conspiracy against me 5%

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quasicontinuous, lying between dichotomous and continuous (Van Os & Verdoux, 2003). An important implication if the continuum perspective is correct is that researching non-clinical delusional ideation can inform the understanding of clinical phenomena, just as studying anxious or depressive states can inform the understanding of emotional disorders. On the basis of a review of 15 studies, Freeman (2006) concludes that there is clear evidence that the rate of delusional beliefs in the general population is higher than that of psychotic disorders (i.e. that delusions occur in individuals with experiences that have not been diagnosed as psychosis). The frequency of delusional beliefs in nonclinical populations varies according to the content of the delusion studied and the characteristics of the sample population (e.g. age structure, level of urbanicity). Approximately 1–3% of the non-clinical population have delusions of a level of severity comparable to clinical cases of psychosis. A further 5–6% of the non-clinical population have a delusion of less severity. Although less severe, these beliefs are still associated with a range of social and emotional difficulties. A further 10–15% of the non-clinical population have fairly regular delusional ideation. For example, Jim van Os and colleagues studied delusions in the large epidemiological Netherlands Mental Health Survey and Incidence Study (NEMESIS). In the sample, 2.1% received a DSM-III-R diagnosis of non-affective psychosis. However, a greater proportion had a ‘true’ psychiatrist-rated delusion (3.3%), or had a ‘clinically not relevant delusion’ (8.7%) defined as the person not being bothered by the belief and not seeking help for it. A separate group of people had endorsed a delusion item but these beliefs were considered plausible or founded (3.8%). Many studies do not differentiate between delusion sub-types, and therefore it is harder to estimate the prevalence of persecutory thinking in particular. In Table 3 studies that include details of the occurrence of paranoid thinking are displayed. A conservative estimate is that 10–15% of the general population regularly experience paranoid thoughts, though such figures hide marked differences in content and severity. It is also likely that the studies underestimate the true frequency of paranoid thoughts because large epidemiological studies from a psychiatric perspective are unlikely to record more plausible fleeting everyday instances of paranoid thinking. Johns et al. (2004) report findings from a British survey of over eight thousand people. Individuals with probable psychosis were removed from the study results. The assessment of delusions was fairly rudimentary: there was no assessment of conviction, differentiation between real or unfounded events, or consideration of clinical severity. However the results are still striking. 20% had thought in the past year that people were against them at times, and 10% felt people had deliberately acted to harm them. The least plausible paranoid item, fears of a plot, was endorsed by 1.5% of this non-clinical population. So although this study does not provide robust data on the presence of delusional beliefs, it does indicate that thoughts of a paranoid nature are common in the non-clinical population. Interestingly, there is evidence from more elaborate epidemiological research that the distribution of paranoid thinking in the general population is continuous and that odder, less plausible paranoid thoughts build upon commoner, more plausible ones, indicating a hierarchical structure to paranoia (Freeman, Garety, Bebbington, Smith et al., 2005) (see Fig. 1). It is clinically noteworthy that a number of studies have found delusions in the general population to be associated with distress and significant impairment in work, family and social functioning (e.g. Olfson et al., 2002). The prevalence figures indicate that there is a need for literature on paranoid thinking that is aimed at the general population and is not focussed on severe mental illness (Freeman, Freeman & Garety, 2006). They are also consistent with the idea of paranoid thoughts being an appropriate strategy that can, in particular circumstances, become excessive, just like anxious thoughts. Consideration of the potentially hostile intentions of others can be a highly intelligent and appropriate strategy to adopt. Walking down certain streets can feel threatening. Friends are not always good friends. As Francis Bacon (1612) noted: ‘What would men have? Do they think that those they employ and deal with are Saints? Do they not think they will have their own ends, and be truer to themselves than to them?’ Whether to trust or mistrust is a judgement that lies at the heart of social interactions and one that is prone to errors. It has been seen that studies using traditional psychiatric assessments find that non-clinical populations experience delusions. Therefore it is reasonable to assume that they are indeed the same phenomena as seen in clinical populations. There is also other evidence consistent with the idea that clinical and non-clinical experiences are linked. Non-clinical symptoms are associated with an increased likelihood of being diagnosed with a psychotic disorder (Eaton, Romanoski, Anthony, & Nestadt, 1991; Van Os, Hanssen, Bijl, & Ravelli, 2000). In particular, Van Os et al. (2000) found that plausible symptoms, secondary symptoms and non-clinically relevant symptoms were all very strongly associated with the presence of clinical symptoms. Moreover, non-clinical and clinical experiences were associated with the same demographic and clinical risk factors (e.g. urban dwelling, living alone, depression). The authors view this as evidence of ‘aetiological continuity’ (see Myin-Germeys, Krabbendam, & van Os, 2003). There is also important evidence that non-clinical symptoms are predictive of the later development of psychosis (Chapman,

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Fig. 1. The paranoia hierarchy.

Chapman, Kwapil, Eckbald, & Zinser, 1994; Poulton et al., 2000). The evidence is substantial enough to conclude that studying non-clinical paranoid experiences will inform the understanding of clinically severe persecutory delusions. Finally, it should be highlighted that, while it has been established that paranoid thinking is a significant topic, there is considerable work to be done on its epidemiological study. Consideration needs to be given to the multi-dimensional nature of the experiences, using assessments that separate the occurrence of such thinking from levels of belief conviction in the thought and associated distress. Just as importantly, greater consideration needs to be given to the content of the thoughts assessed. Persecutory thinking differs greatly in the nature of the threat and the identity of the persecutors. It has also been shown that specific aspects of the content of paranoid thinking (e.g. the power of the persecutor, the awfulness of the threat) are associated with distress (Boyd & Gumley, in press; Chisholm, Freeman, & Cooke, 2006; Birchwood, Meaden, Trower, Gilbert, & Plaistow, 2000; Freeman et al., 2001; Green et al., 2006). Prevalence by content will differ and there could be important differences in the detailed content of delusional ideation between clinical and non-clinical groups. This level of epidemiological scrutiny of paranoid thinking has not been carried out. 4. Psychological processes and persecutory thinking Can the widespread experience of unfounded paranoid thoughts be explained psychologically? The focus will be on psychological processes that have been empirically investigated in relation to persecutory ideation. Some of the psychological processes (e.g. jumping to conclusions) have more often been investigated in relation to delusions in general, which is a clear weakness for the review. Principal components analysis indicates that sub-types such as paranoia and grandiosity/fantastic delusions may have a degree of independence (Vázquez-Barquero, lastra, Nuñez, Castanedo, & Dunn, 1996) suggesting that there may be non-shared causes, although research on differential causes of delusion sub-types is yet to be carried out. A related methodological point is that most studies do not control for the common co-occurrence of symptoms found in clinical settings (Maric et al., 2004) so that spurious associations with paranoia might be found.

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5. Anomalous experiences ‘the delusional belief is not being held “in the face of evidence normally sufficient to destroy it,” but is being held because of evidence powerful enough to support it’ (Maher, 1974) The American psychologist Brendan Maher (1974, 1988, 2003) emphasises that delusional ideas spring from unusual internal experiences. The argument, simply put, is that odd experiences lead to odd ideas. This is consistent with findings that many people with psychosis have clear anomalous experiences such as hallucinations, thought insertion, and replacement of will, and also a range of more subtle perceptual and attentional alterations in experience (e.g. McGhie & Chapman, 1961) and, often, periods of arousal (e.g. Docherty, Van Kammen, Siris, & Marder, 1978; Hemsley, 1994). For instance, Bunney et al. (1999) found that 67 people with schizophrenia reported significantly more perceptual anomalies, particularly in the auditory and visual modalities, than non-clinical controls. Patient reports included: ‘Things are louder than normal: the TV is louder; other peoples' conversations seem louder,’ ‘Sometimes it seems like everything is coming in, like my brain is a radar for sounds,’ ‘Things in the corner of my eyes often catch my attention. I feel like I see everything at once.’ Kapur (2003) has highlighted the importance of aberrant feelings of salience in delusion formation, which is particularly of note since in this account the abnormal experience itself concerns processes of meaning ascription. Odd internal experiences are clearly present in psychosis, but are they connected with delusions? There are a number of strands of evidence – from patient reports, investigation of delusions and hallucinations over time, and examination of the anomalous experiences of hearing impairment and illicit drug use – concerning this question. Asking individuals with delusions directly about their experiences using a structured interview finds, in two out of three studies, that internal feelings and experiences are more often cited as evidence for the beliefs than external events (Buchanan et al., 1993; Freeman et al., 2004; Garety & Hemsley, 1994). In a study of 100 people with delusions, over half of whom had persecutory beliefs, it was found that non-delusional alternative explanations for the evidence taken for the beliefs were uncommon (Freeman et al., 2004). Internal anomalous experiences were least likely to have an alternative explanation, consistent with the anomalous experiences account; in part, individuals may explain puzzling and confusing anomalous experiences delusionally because they have no alternative explanations to turn to. Individuals in the non-clinical population also have anomalies of experience, such as hallucinations, and these have been found to be associated with delusional ideas (Bell, Halligan, & Ellis, 2006; Freeman et al., 2005a; Van Os et al., 2000). Krabbendam et al. (2004) used longitudinal data from the NEMESIS general population study to show a link between hallucinations and delusions. They found that the risk of developing psychosis is significantly increased if delusional ideation develops after hallucinatory experience, but not if hallucinatory experience occurs after delusional ideation. The authors conclude that their data are consistent with Maher's account in that delusional appraisal of anomalous experiences is important in the development of clinical experiences. Maher highlights how hearing impairments, conceived as an anomalous experience, can lead to paranoid thoughts. In older adults there is some evidence of associations of paranoia and hearing difficulties (Christenson & Blazer, 1984; Cooper & Curry, 1976), although this is not always found (Cohen, Magai, Yaffee, & Walcott-Brown, 2004; Östling & Skoog, 2002). In the NEMESIS general population study, hearing impairment was predictive of the presence of positive symptoms of psychosis 3 years later (Thewissen et al., 2005). Most intriguing perhaps is evidence from the first experimental manipulation study of paranoia. Zimbardo et al. (1981) studied 18 highly hypnotisable students. All were hypnotised; twelve had partial hearing impairment induced, with half being made aware of the source of the impairment, and the remainder had an unrelated posthypnotic suggestion. Individuals who were unaware of their hearing impairment had higher levels of paranoid ideation in a later social interaction compared with the other two groups. This is clearly supportive of the anomalous experiences account of delusions. Receiving more contemporary interest has been the role of illicit drugs and psychosis (e.g. Murray, Grech, Phillips, & Johnsons, 2003). Two studies indicate that anomalies of experience caused by street drugs may be associated with delusional ideas. D'Souza et al. (2004) showed in a double-blind randomised placebo controlled study involving 22 nonclinical individuals that the principal active ingredient in cannabis can cause transient increases in positive symptoms of psychosis and perceptual alterations (distorted time perception, external perception, feelings of unreality, and altered body perception). Participant experiences in this study included ‘I thought you were all trying to trick me by changing the rules of the tests to make me fail,’ ‘I thought you could read my mind, that's why I didn't answer,’ ‘My thoughts were fragmented…the past present and future all seemed to be happening at once,’ ‘I thought I could hear the dripping of the

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i.v. and it was louder than your voice.’ Using experience sampling methodology (repeated self-report assessment of patient experiences during the day) (Delespaul, 1995), Verdoux, Gindre, Sorbara, Tournier, and Swendsen (2003) showed that individuals with raised levels of non-clinical delusional or hallucinatory experience were more likely to have unusual sensorial or perceptual experiences after smoking cannabis (i.e. there is an interaction between psychosis vulnerability and cannabis use). However these studies do not test whether drug-induced anomalies of experience lead to delusional ideas. The anomalous experiences account is a difficult and under-researched area of study. Clearly, anomalies of experience are frequently found in individuals with delusions but the nature of their relationship remains to be tested convincingly. It is the least researched of the areas covered in this review and the literature is somewhat fragmented and lacking in replicated findings. This is surprising since it is a very plausible route to delusional ideas, because individuals often rely on feelings to guide judgements. However the lack of sustained attention is also understandable. Internal anomalous experiences are difficult to detect since it is partly the nature of the problem that they go unrecognised by the experiencer who forms delusional ideas. And an absence of good experimental measures of the processes underlying the anomalies means that self-report remains the main research strategy. There are also conceptual and methodological problems in trying to disentangle perceptions from interpretations. And as has been pointed out by many authors, the anomalous experiences account cannot provide a complete answer to delusion formation. Many people have unusual experiences and do not get delusions. But this argument should not detract from the idea that the nature of some internal experiences may particularly lead to unlikely explanations. 6. Affective processes ‘it is perhaps worthy of notice that the various directions, which the delusions take in paranoia, correspond in general to the common fears and hopes of the normal human being. They, therefore, appear in a certain manner as the morbidly transformed expression of the natural emotions of the human heart.’ Kraepelin (1921) The distinguishing of psychotic and affective disorders is one of the main boundaries in diagnostic classification systems. It is therefore intriguing that psychosis researchers have started to pay attention to the role of affective processes in delusional experience (Birchwood, 2003; Freeman & Garety, 2003). Some researchers have focussed on anxiety, others on depression, schemas and self-esteem, though clearly there is overlap between all these concepts. All the main studies of relevance concern persecutory ideation directly. 6.1. Anxiety Paranoia concerns fear. A number of studies by Freeman and colleagues in both clinical and non-clinical populations have stemmed from their observation that persecutory and anxious thoughts both concern the anticipation of threat; fears of physical, social or psychological harm are apparent both in anxious thoughts (e.g. Eysenck & van Berkum, 1992; Wells, 1994) and in persecutory thoughts (Freeman & Garety, 2000; Freeman et al., 2001). It is argued that anxiety helps create thoughts of a paranoid content, and that anxiety-related processes contribute to the maintenance and distress associated with the experience. At present the evidence for a link between anxiety and paranoia is reasonably strong. Anxiety has repeatedly been found to be associated with paranoid thoughts (Freeman et al., 2005a; Fowler et al., 2006; Johns et al., 2004; Martin & Penn, 2001) and persecutory delusions (Freeman & Garety, 1999; Huppert & Smith, 2005; Naeem, Kingdon, & Turkington, 2006; Startup, Freeman, Garety, in press). Better evidence for the role of anxiety in the development of paranoid thoughts is that anxiety is predictive of the occurrence of paranoid thoughts (Freeman et al., 2003, 2005b) and of the persistence of persecutory delusions (Startup et al., in press). Moreover, it has been shown in non-clinical groups that paranoid thoughts build upon common interpersonal anxieties and worries (Freeman, Garety, Bebbington, Slater et al., 2005; Freeman, Slater, et al., 2003; Freeman, Garety, Bebbington, & Smith et al., 2005c). The most common type of suspiciousness is that of a social anxiety or interpersonal worry theme; ideas of reference build upon these sensitivities; persecutory thoughts are closely associated with the attributions of significance; and as the severity of the threatened harm increases, the less common is the thought. The implication is that severe paranoia may build upon common emotional concerns. More broadly, the hypotheses are consistent with innovative work showing greater stress sensitivity in people with psychosis (Myin-Germeys, Delespaul, & van Os, 2005). Intriguingly, Schulze et al. (2005) report a similar genetic marker for persecutory delusions and anxiety.

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Paranoid thinking and anxiety-related processes have been linked. Initial evidence indicates that almost two-thirds of individuals with persecutory delusions have a worry thinking style (even about matters unrelated to paranoia) (Freeman & Garety, 1999; Startup et al., in press). Worry in individuals with persecutory delusions is associated with higher levels of distress and with delusion persistence. Other anxiety-related processes are also apparent in people with persecutory delusions. An example is safety behaviours (Freeman et al., 2001, 2007). Individuals who feel threatened often carry out actions designed to prevent their feared catastrophe from occurring; this has been termed ‘safety behaviour’ (Salkovskis, 1991). When the perceived threat is a misperception, such as in anxiety disorders and paranoia, there are important consequences. Individuals fail to attribute the absence of catastrophe to the incorrectness of their threat beliefs. Rather, they believe that the threat was averted only by their safety behaviours (e.g. ‘The reason I wasn't attacked was because I left the street in time and made it back home’). Threat beliefs are likely to persist partly due to this failure to obtain and process disconfirmatory evidence. Freeman et al. (2007) found that 96 out of 100 patients with persecutory delusions had used safety behaviours in the past month. In the course of their work, Freeman and colleagues have collaborated with computer scientists to develop, using virtual reality (VR), the first method to study persecutory ideation in the laboratory (Freeman et al., 2003, 2005b). With virtual reality the environment is controlled; individuals can therefore enter an identical situation, and so appraisals for the same event can be assessed and psychological factors associated with particular appraisals identified. In applying this method to the study of persecutory ideation, virtual characters (‘avatars’) in a virtual environment can be programmed to exhibit only behaviour that most people would assess as neutral. Individuals' appraisals of the avatars can then be assessed, and the psychological factors that lead some individuals to have (clearly unfounded) persecutory thoughts determined. In the studies, most people found that the virtual library environment used neutral or even positive. However about a third had persecutory thoughts about the avatars. In both published studies, anxiety and interpersonal sensitivity were predictors of unfounded persecutory ideation in virtual reality. However, these authors also note the important task of identifying differential predictors of anxiety and paranoia. They carried out the first study investigating this issue by not only measuring persecutory thoughts in VR but by also assessing social anxiety thoughts about the avatars. Interestingly, the prediction of persecutory ideation and social anxiety in virtual reality shared many of the same factors – and this is unsurprising given the similarities in their threat content – but what sets apart the prediction of persecutory ideation from that of social anxiety was the presence of predisposition to hallucinatory experience. The findings support the view that emotional disturbance can lead to social anxiety but that the addition of anomalous experiences such as hallucinations makes persecutory ideation more likely. 6.2. Depression, self-esteem and schemas The issue of the relationship between paranoia and emotion is more controversial when it concerns depression and self-esteem. Richard Bentall, a leading pioneer of the research field, argues that persecutory delusions are a defense against negative affective processes (Bentall et al., 1994; Bentall et al., 2001). In contrast, Freeman and colleagues put forward the view that persecutory delusions are a direct reflection of emotional concerns (Freeman et al., 2002; Freeman et al., 2004; Freeman et al., 2005c). Trower and Chadwick (1995) argue that there are two quite distinct forms of paranoia, one of which is a defense (Poor Me paranoia) and the other of which is a direct reflection of extreme negative emotion (Bad Me paranoia). It is worth noting that some delusion-as-defense theories focus on the avoidance of negative self-esteem and some focus on the avoidance of depression, but, nonetheless, negative self-esteem and depression are typically found to correlate in studies of persecutory delusions (Chadwick, Trower, Juusti-Butler, & Maguire, 2005; Drake et al., 2004; Freeman et al., 1998, 2001; Lyon, Kaney, & Bentall, 1994). A simplified view would be that if delusions are a defense then self-esteem should be normal but if paranoia builds on negative views of the self then self-esteem should be low. Bentall et al. (2001) consider the self-esteem data and argue that there are very mixed findings concerning levels of self-esteem in paranoia, with some studies finding low self-esteem and some preserved self-esteem. Their explanation for this is that there is instability in self-esteem in people with paranoia, and that these individuals are locked into a struggle to defend against negative emotion, sometimes winning, sometimes losing (which clearly makes the theory harder to test). There is, however, perhaps a clearer, less complicated picture apparent in the self-esteem and paranoia data, which will now be described. There are actually few studies that simply look at current levels of self-esteem in individuals with current persecutory delusions compared with a matched non-clinical control group. And the number of patients in these studies is small and most likely comprises unrepresentative samples. Studies of paranoia in the non-clinical

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population provide much better information on the issue because they include a much larger number of participants, have a greater range in paranoia scores compared to clinical groups because of the dimensional approach adopted, and avoid the complications of the effects of being a patient with psychosis on self-esteem and depression (e.g. receiving a diagnosis, compulsory treatment, medication, unemployment, stigma). The findings in non-clinical populations are clear: paranoia is repeatedly found to correlate with lower self-esteem and higher depression (Ellett, Lopes, & Chadwick, 2003; Freeman et al., 2005a; Fowler et al., 2006; Johns et al., 2004; Martin & Penn, 2001; McKay, Langdon, & Colheart, 2005). For instance, in a representative population survey of over eight thousand people in the UK, Johns et al. (2004) found that paranoid thinking was associated with symptoms of anxiety and depression, victimisation experiences, and recent stressful life events. The finding of an association of lowered selfesteem and paranoia is not unique to non-clinical groups. Drake et al. (2004) in a study of approximately two hundred first episode patients found paranoia to be associated with depression and lower self-esteem at several time points over 18 months. Furthermore, this study fits within a larger literature indicating an association of affective problems with the positive symptoms of psychosis (e.g. Freeman, 2006; Guillem et al., 2005; Norman & Malla, 1994; Sax et al., 1996) and evidence that low self-esteem and anxiety predict the later development of positive symptoms of psychosis (Krabbendam et al., 2002). So what do these findings indicate? Unless self-esteem is considered as the only cause of paranoia then there is no reason to expect everyone with paranoia to have the same level of self-esteem (it might even be considered an odd finding). But what is clear from the self-esteem data is that there is in general an association of paranoia with lowered self-esteem and depression. The distribution of self-esteem and mood is skewed towards the negative in paranoia, which would not be expected if persecutory thoughts serve as a defense. Many individuals with paranoia have lowered self-esteem but some do not. But of course there is the difficulty of determining the causal direction of the association. It is entirely plausible that having paranoid thoughts would lower mood and self-esteem. Experimental studies examining causal issues are needed. It is most likely that there is a circular relationship, with low self-esteem and depression being one of a number of vulnerability factors for paranoia, which then decreases self-esteem and increases depression further. But the debate about global self-esteem and paranoia may obscure the important point. Self-esteem may not be the key concept when considering paranoia; rather it is specific negative beliefs about the self and others that are important (Chadwick et al., 2005; Freeman et al., 2002; Fowler, 2000; Fowler et al., 2006; Garety et al., 2001). In both non-clinical (Freeman et al., 2003, 2005b) and clinical studies (Fowler et al., 2006; Smith et al., 2006), paranoia has been found to be associated with negative self-beliefs and sensitivities. In what is likely to prove a key paper in the area, David Fowler et al. (2006) found that in a non-clinical population of over seven hundred students paranoia was associated with negative beliefs about the self, negative beliefs about others, less positive beliefs about others, and anxiety. Self-esteem as traditionally measured was not as good a predictor of paranoia and, unlike schematic beliefs, did not discriminate between the non-clinical group and a group of two hundred and fifty patients with psychosis. Of course, negative schematic beliefs are related to self-esteem, but they are not exactly the same (Fowler et al., 2006). When specific negative beliefs are considered, and the exact content may vary in the individual case, then links with paranoia are more likely to be found. This fits with Christine Barrowclough et al. (2003) arguing that self-esteem needs to be assessed in a very detailed interview to find links with symptoms of psychosis. However, just as with depression and schema, there is a clear problem in establishing the direction of causal effects in the relationship between paranoia and schematic beliefs. It is likely to be a circular effect. The parsimonious explanation of associations of negative self beliefs, lowered self-esteem and depression with clinical and non-clinical paranoia is that they are directly associated, without the need to evoke defensive processes. But a stricter test of defense theories of paranoia would be whether covert self-concept is lower than overt presentations (i.e. there is discrepancy between core beliefs about the self and those in conscious awareness). Clearly it is a methodological difficulty to penetrate hypothesised defenses and a negative finding could always be interpreted as a failure of methodology rather than theory. It has been argued that the emotional Stroop task is currently the most plausible defense-penetrating task (Garety & Freeman, 1999; Smith, Freeman, & Kuipers, 2005). The delusion-asdefense model would predict biases towards negative self-concept words using the Stroop but for overt self-esteem to be comparable to controls. However, even the first step of showing biases towards depressive words has not been shown in some studies (Bentall & Kaney, 1989; Fear, Sharp, & Healy, 1996), and discrepancy with overt self-esteem using this method has not been demonstrated. Evidence for a discrepancy has rested on one particular method using

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two different measures of attributions (Lyon et al., 1994) but there have been failures to replicate with this particular methodology (Kristev, Jackson, & Maude, 1999; Martin & Penn, 2002; McKay et al., 2005; Peters & Garety, 2006). Moreover, it is of methodological note that in none of the attribution studies has the crucial test of discrepancy between attribution measures at an individual level been tested statistically. Instead the studies have simply looked at patterns of results at a group level for each measure. Even in grandiose delusions, where the delusion might be more likely to protect the self, evidence of discrepancy between overt and covert self-esteem is lacking (Smith et al., 2005). Can it simply be that there are two distinct sub-groups of paranoia as suggested by Trower and Chadwick (1995)? No systematic empirical tests have been made of this interesting theoretical account; most obviously, there has been no comparison of overt and covert self-esteem in Poor Me and Bad Me paranoia groups. There are only two empirical lines of evidence directly related to the theory. Unsurprisingly, Bad Me paranoia is associated with greater depression and negative self-esteem than Poor Me paranoia (Chadwick et al., 2005; Freeman et al., 2001). But it also seems that cases of Poor Me paranoia may be uncommon; Fornells-Ambrojo and Garety (2005) found only three cases of Bad Me paranoia in 40 individuals with early episode psychosis and paranoia. An alternative account of the current evidence is that the concept of deservedness is an important (dimensional) aspect of the content of paranoia associated with distress, but not an indicator of discrete categories with opposite causes. In summary, when understanding paranoia it may be better to think in terms of specific schematic beliefs rather than global self-esteem. Paranoia may well often build on negative ideas about the self, others and the world. If the measure is appropriate then paranoia is often associated with self-concept concerns, which are in general apparent in people with paranoid thoughts. Schematic concerns may provide content to paranoid thoughts but perhaps not affect conviction in the thoughts to a large degree. If negative self-esteem is present then it may be particularly associated with the distress of paranoid experience. Overall there is now considerable evidence of affect and related processes having a direct, nondefensive, role in the development of paranoid thoughts. Anxiety may be especially important in paranoid thoughts. However, causal tests of hypothesised factors are now needed. It is also of note that psychological factors such as social rank, power differentials and submissive behaviours have been studied in pioneering studies of the distress of auditory hallucinations but are yet to be fully applied to paranoia and may be another important element in understanding the experience (Freeman et al., 2005c; Gilbert, Boxall, Cheung, & Irons, 2005). 7. Reasoning ‘The degree of paranoia stifled my ability to live and think freely. False suspicions impeded my progress in going forward. Once I began to question, my suspicions could not be verified. Once I acknowledged that there were holes of uncertainty, I began to think that some of my thoughts might be delusional even though they had the appearance of truth and believability. As each day passed and I wasn't killed, I dug deeper at my own scared pace.’ Chapman (2002). Robert Chapman (2002) describes his determined recovery from delusions using a self-devised four-step strategy of doubting paranoid beliefs, recognising and identifying delusional thoughts, processing disconfirmatory evidence, and considering alternative explanations. His approach is based upon testing delusional beliefs using reasoning strategies. If delusions are incorrect – or perhaps, more importantly, uncorrected – beliefs, then judgemental or reasoning processes are inherently implicated in their cause. A number of researchers have therefore tried to identify biases or deficits in reasoning in individuals with paranoia. 7.1. Jumping to conclusions Reasoning had long been assumed to be awry in people with delusions, but empirical evidence for this view had not been forthcoming. In innovative work from the late 1980s onwards, Philippa Garety and colleagues provide empirical evidence that individuals with delusions ‘jump to conclusions’ (JTC). In an experimental probabilistic reasoning task individuals are required to decide from which of two hidden jars coloured beads are being drawn. The jars both contain beads of two different colours but the proportion of beads of each colour in the jars is reversed. Typically, one jar will contain 85 black beads and 15 yellow beads and the other jar will contain 85 yellow beads and 15 black beads. It has been found that individuals with delusions request fewer pieces of information (i.e. to see fewer beads drawn from the jar) before making a decision compared with non-clinical controls (see review by Garety and Freeman, 1999). Such a bias in data gathering is hypothesised to lead to the rapid acceptance of beliefs even if there is limited evidence to

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support them, and hence be a factor in delusion development and maintenance. Probabilistic reasoning has rarely been studied in relation to delusion sub-type. In Table 4 studies of probabilistic reasoning are summarised but with an emphasis on the presence of persecutory delusions in the samples. Only studies that allow the participants to gather data freely are reported. Remarkably, in all ten clinical studies where individuals with delusions are compared with non-clinical controls on the number of draws to decision in probabilistic reasoning tasks, data gathering is hastier in the delusion group. Such replication of a finding is rare in psychosis research and is firm evidence for the presence of a JTC bias in individuals with delusions. One half to two-thirds of individuals with delusions jump to conclusions (defined as making a decision after two or fewer beads). A study of one hundred individuals with delusions indicates that JTC may be particularly associated with delusional conviction (Garety et al., 2005). But is the bias apparent in people with persecutory delusions? This is much less clearly shown by the studies. In only seven studies is information on the presence of persecutory delusions available. Individuals with persecutory delusions were the focus of only one study (Startup, 2004) and were present in at least half the participants in the other six studies. The limited conclusion that can be made at present on this information is that JTC is often present in people with persecutory delusions. However, there have been no tests of specific associations with delusion sub-types. In most cases individuals with persecutory delusions would have had other delusion beliefs and therefore whether JTC is more strongly associated with another delusion sub-type such as grandiose delusions remains to be investigated. The evidence base on JTC concerns individuals with current delusions. However, there are two intriguing recent studies of JTC in groups that are not currently deluded. Broome et al. (in press; pers. com.) found evidence that hasty data gathering is present in a group identified as at risk of developing psychosis, indicating that the bias may be present before delusions occur, although it was only in the more difficult versions of the reasoning task that JTC was apparent. JTC may be a cause of delusions. In an important study, Van Dael et al. (2006) studied JTC in individuals with psychosis and their relatives, and individuals in the general population high or low in non-clinical psychotic symptoms (i.e four groups differing in levels of delusional ideation and vulnerability to psychosis). Hasty data gathering was associated with both delusional ideation and psychosis liability. As the authors argue, JTC may be both partly a trait factor reflecting liability for psychosis and partly a state factor as it covaries with level of delusional ideation. In other words, JTC could contribute to both delusion formation and maintenance. Consistent with this work, two studies have found JTC in individuals whose delusions have remitted (Mortimer et al., 1996; Moritz and Woodward, 2005), although one study did not (Peters & Garety, 2006). Colbert and Peters (2002) found evidence of JTC in non-clinical individuals with high delusional ideation compared with individuals with low clinical delusional ideation, but this was not replicated by Van Dael et al. (2006). Furthermore, in the only non-clinical study to examine an association of JTC and paranoid thinking, there was no evidence for such a link (Freeman et al., 2005b). Biases in reasoning may be much more subtle outside of acute delusional states. In addition to the exact relationship of JTC to the development of delusions, the cause of hasty data gathering itself remains to be determined. There have been a number of speculations: Dudley and Over (2003) note the need to consider the goal of reasoning; Moritz and Woodward (2004) raise the issue of the level of the threshold at which an explanation is accepted; the belief confirmation bias (Freeman, Garety, McGuire, & Kuipers, 2005) or a bias against disconfirmatory evidence (Moritz & Woodward, 2006b) may be related to JTC; and data gathering is likely to be influenced by the availability of alternative explanations for experiences (Freeman et al., 2004). Previous suggestions that JTC reflects a generalised need for closure have been discounted however (Freeman, Garety, Kuipers, Colbert, Jolley et al., 2006). Biases in data gathering will plausibly affect belief formation and maintenance, enabling the rapid acceptance of implausible explanations. However, it should also be noted that a JTC bias might distort the evidence. For example, Moritz and Woodward (2006a) suggest that JTC may lead to acceptance of false memories or knowledge corruption, while misattribution biases hypothesised to be important in the occurrence of hallucinations have been found to be associated with delusional ideation (e.g. Johns et al., 2006; Allen, Freeman, Johns, & McGuire, 2006). The complexity is that reasoning biases may contribute to the anomalies of experiences that are taken as the evidence for delusional beliefs. Future studies will benefit from not considering data gathering in isolation. More detailed experimental work is needed on the interaction of the production of potential explanations, data gathering, the processing of confirmatory and disconfirmatory reasoning, the acceptance of explanations, and how beliefs change. Furthermore, how these are modified by current goals, emotional state, and interactions with others needs to be examined. Causal studies of

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Table 4 Jumping to conclusions (as assessed by the probabilistic reasoning task) Study

Groups of participants

15 delusions 10 psychiatric control 15 non-clinical controls Garety et al. (1991) 27 delusions 14 anxious 13 non-clinical control Mortimer et al. (1996) 43 patients with schizophrenia

Dudley et al. (1997a)

Dudley et al. (1997b)

15 delusions 15 depression 15 non-clinical controls 15 delusions of persecution or grandeur 16 depression 15 non-clinical controls

Task

Jumping to conclusions Comments as assessed by draws to decision (in delusion groups compared with non-clinical controls)

?

85:15 beads ratio

✓

?

85:15 beads ration

✓

?

85:15 beads ratio

73% (Dudley, pers. com).

85:15 and 60:40 beads ✓ ratios

73% (Dudley, pers. com)

60:40 neutral word stimuli ✓ ratio 60:40 emotionally salient word stimuli ratio 85:15 beads ratio ✓

The delusion group requested fewer words in both versions of the task. Emotionally salient stimuli reduced data gathering in all three groups.

85:15 beads ratio

✓

60:40 beads ratio

✓

The beads task was administered four times and average scores used. 70% of the delusion group and 10% of the control group jumped to conclusions defined as a decision after two beads or fewer. 50% of the delusion group showed jumping to conclusions defined as deciding after two beads or fewer. 10% of the control group showed JTC.

Fear and Healy (1997) 30 delusions ? 16 obsessional and delusional features 29 obsessive-compulsive disorder 30 non-clinical controls Conway et al. (2002) 10 delusions 50% 10 non-clinical controls

Startup (2004)

28 Persecutory delusions 30 Non-clinical participants

100%

55% of the delusion group jumped to conclusions (two beads or fewer). 11% of the non-delusion participants showed JTC. The study did not include a control group and therefore it is unknown whether the clinical group shows hasty data gathering in relation to non-clinical controls. It is not known how many of the participants had delusions. 42% of the sample were reported as jumping to conclusions defined as deciding after one bead has been drawn. The delusion group requested fewer beads in both versions of the beads task.

73% of the delusion group showed jumping to conclusions as defined by deciding after one bead. 20% of the non-clinical control group jumped to conclusions.

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Delusion studies Huq, Garety, and Hemsley (1989)

Proportion delusion group with persecutory beliefs

Moritz and Woodward 17 delusions (2005) 14 schizophrenia and no current delusions 28 psychiatric controls 17 non-clinical controls

61%

85:15 beads ratio

✓

85:15

✓

100 delusions

Peters and Garety (2006)

23 delusions 22 psychiatric controls 36 non-clinical controls

Van Dael et al. (2006)

40 individuals with ? schizophrenia 40 first degree nonpsychotic relatives 41 non-clinical individuals with psychotic experiences 53 non-clinical controls

Non-clinical studies Colbert and Peters (2002)

Freeman, Garety, Bebbington, Slater et al. (2005)

85:15, 60:40 beads ratios. 60:40 emotionally salient word stimuli task also used

85:15, 60:40 and 44:28:28 beads ratios

17 non-clinical individuals 85:15 beads ratio high in delusional ideation 17 non-clinical individuals low in delusional ideation 30 non-clinical individuals Scorers across the full range of 85:15 beads ratio non-clinical paranoia

✓

Defining JTC as making a decision after two or fewer beads, 65% of the delusion group, 43% of the no current delusions schizophrenia group, 21% of the psychiatric controls and 6% of the non-clinical controls showed JTC.

A non-clinical control group was not included in this study. With JTC defined as making a decision after two beads or fewer: 53% showed JTC on the 85:15 tasks 41% showed JTC on the 60:40 task 37% showed JTC on the emotionally salient words task. It is also of note that in this study the groups were followed up over time. Individuals with delusions that had remitted did not differ from non-clinical controls in data gathering. Jumping to conclusions (defined as deciding after one bead) was found in 32.5% of the individuals with schizophrenia; 25% of the relative group; 14.6% of the non-clinical high symptom group; and 11.3% of the control group.

JTC was associated with delusional ideation and psychosis liability across the groups. The ‘at risk’ group showed hasty data gathering on the two more difficult beads ratio tasks (but not the 85:15 task). Draws to decision were correlated with delusional conviction in all participants.

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90:10 beads ratio

Garety et al. (2005)

Broome et al. (in press; 31 at risk of psychosis pers. com.) 23 non-clinical controls

✓

100% All participants had at least mild paranoid ideation/suspiciousness as assessed with the Brief Psychiatric Rating Scale item 11 (Moritz, pers. Comm.). 70% (SAPS N2)

✓

X

There was no evidence of jumping to conclusions being associated with paranoid thoughts in an experimental situation.

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reasoning and delusional ideation are clearly indicated now. This work has relevance for the study of delusional beliefs but also more generally for cognitive therapy approaches to problems where changes in beliefs are targeted. 7.2. Attributional style The literature on attributional style developed by Richard Bentall and colleagues has been closely linked to the delusion-as-defense theory, but attributional style need not be tied to such a theoretical framework; if a person tends to explain events in terms of other people then this would be a plausible factor in the creation of paranoid thoughts, without evoking the further hypothesis that the explanation serves to defend the self-concept. This means that the key issue is not whether individuals with delusions have a self-serving bias (i.e. differences in the types of attributions given for positive and negative events) but, given the negative content of paranoid thoughts, whether external attributions for negative events are made. Snyder's (2006) account of his paranoid episode illustrates a strong bias to explain events in a particular way: ‘My concept of THEM grew and began to colour every experience I had. After a few months, everything that happened to me was somehow related to THEM, or was caused by THEM. When I started experiencing problems with my home computer, I blamed THEM. When I got a parking ticket, it was THEIR influence with the police that got me into trouble. Every thought that I had was somehow associated with THEM.’ Most attribution studies have used either the Attributional Style Questionnaire (ASQ) (Peterson et al., 1982) or the Internal, Personal and Situational Attributions Questionnaire (IPSAQ) (Kinderman & Bentall, 1996a). The basic design of these questionnaires is similar. A hypothetical event is described (e.g. ‘You go on a date and it goes badly’) and the participant is asked to note a cause and then rate it for how much the cause is due to something about them or to something about other people or circumstances. The results of these studies are summarised in Table 5. Three ASQ studies (Fear et al., 1996; Krstev et al., 1999; Lyon et al., 1994) show clear evidence of an externalising bias for negative events in people with persecutory delusions compared with non-clinical controls and two ASQ studies find no differences between persecutory delusion and non-clinical control groups (Kinderman, Kaney, Morley, & Bentall, 1992; Martin & Penn, 2002). None of the four IPSAQ studies finds evidence of an externalising bias for negative events in persecutory delusion groups compared with non-clinical controls (Kinderman & Bentall, 1996b; Martin & Penn, 2002; Randall, Corcoran, Day, & Bentall, 2003; McKay et al., 2005). In the first clinical study using the IPSAQ, Kinderman and Bentall (1996b) found that, when external attributions were made, individuals with persecutory delusions were more likely to make external–personal attributions compared to non-clinical controls (who were more likely to make external–situational attributions). However, this has not been replicated in three further clinical studies (Martin & Penn, 2002; McKay et al., 2005; Randall et al., 2003). In studies of non-clinical paranoid ideation in student groups only one of three studies finds an association of paranoia and a personalising bias (Kinderman & Bentall, 1996a). Overall, four out of nine studies using the two attribution measures indicate that there are differences between individuals with persecutory delusions and non-clinical controls in attributions for negative events. Therefore, the empirical case for persecutory delusions being associated with an excessive externalising style for negative events is unconvincing at present. A large-scale study is needed, but it will be important to control for both grandiosity and depression since there is evidence for their association with attributional style (e.g. Jolley et al., 2006). However, it should be noted that the questionnaire assessments of attributional style used may limit the chances of finding evidence of an externalising style. There are concerns over the psychometric properties of questionnaires such as the ASQ (e.g. Krstev et al., 1999) and anecdotal reports indicate that participants have difficulties completing the attribution questionnaires. Perhaps most importantly, clinical experience indicates that the questionnaires do not assess the types of events that delusional attributions concern. Delusions often concern ambiguous social events (e.g. the look on a face, the gesture of a person) and, as discussed earlier, confusing internal experiences. The ASQ was designed for depression research and does not assess these sorts of experiences. 7.3. Theory of mind Individuals with persecutory ideation are by definition sometimes misreading the intentions of other people. Therefore a candidate cause is the mechanism of determining others' mental states. Drawing upon established research into children's understanding of ‘folk psychology,’ and drawing a close analogy with autism, Frith (1992, 2004) proposes that symptoms of schizophrenia develop from newly acquired difficulties in a person's ‘theory of mind’ skills (ToM) (Premack & Woodruff, 1978). ToM refers to the ability to understand mental states (beliefs, desires, feelings,

Table 5 Attributional style for negative events (assessed by the ASQ or IPSAQ) Study

Clinical psychosis studies Kinderman et al. (1992)

Attributional measure Externalising bias for Comments negative events (in delusion group compared with non-clinical controls).

23 persecutory delusions 21 psychiatric control 28 non-clinical control

ASQ

X

15 persecutory delusions 15 persecutory delusions and depression

ASQ

?

ASQpf

✓

ASQ

✓

ASQ

✓

ASQpf

X

15 depression

Lyon et al. (1994)

Fear et al. (1996)

Sharp et al. (1997)

Krstev et al. (1999)

14 persecutory delusions 14 depression control group 14 non-clinical control 20 persecutory delusions 9 non-persecutory delusions 20 non-clinical controls 19 persecutory and/or grandiose delusions (14 persecutory, 5 grandiose) 12 somatic or jealousy delusions 24 non-clinical controls 62 individuals with first episode psychosis, but none held a persecutory delusion at the time of testing

From graphed data it appears from visual inspection that the delusion group score comparably to the non-clinical group on attributions for negative events. The depressed group, however, makes more internal ratings for negative events. This study did not include a non-clinical control group and therefore the presence of an externalising bias in individuals with persecutory delusions cannot be tested. In comparison with depressed patients, individuals with persecutory delusions made more externalising attributions for negative events, but this could be due to people with depression showing an internalising bias. Attributions were associated with levels of depression and paranoia. Higher depression was associated with more internalising. Higher paranoia was associated with more externalising. In this study a new parallel version of the ASQ was used.

The externalising style was present in both individuals with persecutory delusions and individuals with non-persecutory delusions (mainly grandiose). Externalising specific to persecutory/grandiose group and not to other delusion sub-types.

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Candido and Romney (1990)

Groups of participants

The parallel version of the ASQ developed by Lyon et al. (1994) was used. The authors did not include a non-clinical control group. They compared their results with other studies to argue that an excessive externalising bias for negative events is not apparent. Higher levels of depression were associated with more internalising, while higher levels of suspiciousness were associated with less internalising for negative events. (continued on next page) 441

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Clinical psychosis studies Jolley et al. (2006)

Groups of participants

Attributional measure Externalising bias for Comments negative events (in delusion group compared with non-clinical controls).

7 persecutory delusions 23 persecutory delusions and depression 7 persecutory and grandiose delusions

ASQ

?

ASQ IPSAQ

X X

IPSAQ

X

34 non-persecutory delusions psychosis

Martin and Penn (2002)

Kinderman and Bentall (1996b)

15 persecutory delusions 15 non-persecutory delusions schizophrenia group (9 had no delusions) 16 non-clinical control 20 persecutory delusions

20 psychiatric control

20 non-clinical

The absence of a non-clinical control group prevents determination of whether an externalising bias was present. However there were group differences in externalising for negative events. Individuals with persecutory and grandiose delusions were more likely to externalise negative events than the persecutory delusions and depression group and the non-persecutory delusions group. In the whole sample, the presence of both grandiosity and persecutory delusions was associated with externalising attributions for negative events and not persecutory delusions or grandiose delusions on their own. Using two measures of attributions there was no evidence of either excessive externalising or personalising attributions in individuals with persecutory delusions based upon their self-report. The persecutory delusion group scored comparably to the non-clinical group for whether an external attribution was made for a negative event. However, when an external attribution was made, the persecutory delusion group was more likely to make a personalising attribution than the non-clinical control group. The non-clinical control group was more likely to make situational external attributions than the persecutory delusions group. Paranoia scale scores were not correlated with the tendency to personalise external attributions. Depression scores were associated with internal but not personalising attributions.

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Table 5 (continued ) Study

19 persecutory delusions 14 persecutory delusions in remission 18 non-clinical control

IPSAQ

X

There were no differences in internal, personal, or situational attributions for negative events for the three groups as self-rated.

McKay et al. (2005)

Study 2 13 persecutory delusions

IPSAQ

X

19 persecutory delusions 15 non-persecutory delusion schizophrenia group (nine had no delusions) 21 non-clinical controls

IPSAQ

?

The persecutory delusion group made more internal attributions for negative events than the control group (accounted for by levels of depression). All groups had comparable scores for level of personalising attributions for negative events. The control group made more situational attributions for negative events than the persecutory delusion group (accounted for by levels of depression). The groups were not compared on the numbers of internal attributions for negative events. However, there were no significant differences in levels of personalising of negative events between the three groups.

Non-psychosis studies Kinderman and Bentall (1996a)

85 non-clinical students

IPSAQ

Martin and Penn (2001)

193 non-clinical students

IPSAQ

McKay et al. (2005)

Study 1: 40 non-clinical students

IPSAQ

Blackshaw et al. (2001)

25 individuals with Asperger syndrome 18 non-clinical control group

IPSAQ

12 remitted persecutory delusions group 19 non-clinical controls

Langdon et al. (2006)

Higher levels of non-clinical paranoid ideation were associated with making personalising external attributions. Depression was associated with making internal attributions. Higher levels of non-clinical paranoid ideation were not associated with a personalising bias for negative events. No association of persecutory ideation and attributional style was found. A drawback for interpretation of this study is that the authors use an unpublished novel measure of persecutory ideation. Individuals with Asperger syndrome had higher levels of paranoia than the control group but did not differ significantly in the presence of a personalising bias for negative events.

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Randall et al. (2003)

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and intentions) in the self or others. Previously, Cameron (1959) observed that people vulnerable to paranoia are “unable to understand adequately the motivations, attitudes, and intentions of others.” Frith argues that delusions of persecution and reference arise from the person with schizophrenia knowing that people have mental states that cannot be directly viewed, but making invalid attempts at inferring them. According to Frith, delusions of reference occur because a person with schizophrenia mistakenly labels an action as having an intention behind it. Persecutory delusions arise because the person notices that other peoples' actions have become opaque and surmises that a conspiracy exists. Frith's innovative research has led to a large literature in which tasks assessing different levels of ToM abilities have been used with people with schizophrenia. Indeed this is now the most researched psychological process and psychosis, and it could be argued that an association of ToM performance and paranoia has been more stringently tested than the other psychological factors reviewed. There is a consensus that ToM difficulties are apparent in people with a diagnosis of schizophrenia, and may be most severely present in individuals with negative symptoms and incoherent speech (Brüne, 2005; Garety & Freeman, 1999; Harrington, Langdon, Seigert, & McClure, 2005; Harrington, Siegert, & McClure, 2005; Sarfati, Hardy-Baylé, Besche, & Widlöcher, 1997). Indeed, this association with negative symptoms may be expected from the neuropsychological literature; ToM tasks and executive functioning have been found to be linked in the developmental psychology literature (e.g. Hughes, 2002) and executive functioning difficulties have been found to be associated with negative symptoms and thought disorder but not the positive symptoms of psychosis (e.g. O'Leary et al., 2000). Difficulties with ToM may be a trait factor associated with liability to psychosis (Janssen, Krabbendam, Jolles, & van Os, 2003). As Frith (2004) notes, however, the ToM findings for paranoia may be more equivocal. In Table 6 ToM studies are listed that include a comparison of individuals with predominately paranoid symptoms and non-clinical controls, or that examine correlations between positive symptoms and ToM performance. It is clear that ToM problems do occur in people with predominately paranoid symptoms. In eight studies ToM performance in people with paranoid symptoms is poorer relative to controls (Corcoran, Cahill, & Frith, 1997; Corcoran, Mercer, & Frith, 1995; Craig, Hatton, Craig, & Bentall, 2004; Frith & Corcoran, 1996; Harrington, Langdon, Siegert, & McClure, 2005; Langdon, Corner, McLaren, Ward, & Coltheart, 2006; Randall et al., 2003; Russell, Reynaud, Herba, Morris, & Corcoran, 2006). There is only one failure to replicate (Pickup & Frith, 2001). However, ToM problems are not necessary for paranoid experiences. Walston, Blennerhassett, and Charlton (2000) set out to deliberately recruit a highly selected pure persecutory delusion group from psychiatric services. Four individuals with persecutory delusions but with an absence of other psychopathology, intellectual impairment, overtly illogical or incoherent reasoning, or diagnoses such as depression, mania or schizophrenia were assessed. All four cases showed intact theory of mind performance. Because ToM difficulties have been hypothesised to explain several symptoms of psychosis, the majority of studies have tested a group of people with schizophrenia and examined associations between symptoms of psychosis and ToM performance. It is important to note that this provides a more stringent test than the group division studies because paranoid symptoms in clinical groups are rarely the only symptom present (Maric et al., 2004). Even in the studies that group individuals with paranoid symptoms separately from people with negative symptoms, there may still be low levels of negative symptoms in the paranoid group. The possibility remains that the findings of ToM difficulties in people with paranoid symptoms are actually due to the presence of other symptoms. Most studies do not find an association of positive symptoms of psychosis and ToM performance. In six studies, negative symptoms and/or thought disorder, but not delusions and hallucinations, are associated with ToM difficulties (Kelemen et al., 2005; Langdon et al., 1997; Langdon, Coltheart, Ward, & Catts, 2001; Mitchley, Barber, Gray, Brooks, & Livingstone, 1998; Mazza, De Risio, Surian, Roncone, & Casacchia, 2001; Pickup & Frith, 2001). Roncone et al. (2002) and Russell et al. (2006) found no association of positive or negative symptoms with ToM performance in their sample, although in the Roncone et al. (2002) study a sub-sample was examined controlling for IQ and an association with positive symptoms was found. In two studies positive symptoms were associated with poorer ToM performance (Doody, Götz, Johnstone, Frith, & Cunningham Owens, 1998; Marjoram et al., 2005). Six studies have examined associations with paranoid symptoms in particular. Four found no association of paranoia and ToM abilities (Blackshaw, Kinderman, Hare, & Hatton, 2001; Greig, Bryson, & Bell, 2004; Langdon et al., 1997, 2001) and two studies did find an association (Craig et al., 2004; Harrington et al., 2006). The study of Greig et al. (2004) is the largest study of ToM in schizophrenia and best addresses the question of ToM and psychotic symptoms. 128 outpatients with schizophrenia were assessed on the ability to understand hints. Theory of mind performance was most strongly associated with thought disorder. There was an association of ToM performance with delusions but not the level of persecutory delusions. In a regression analysis it was thought disorder, and not delusions, that predicted ToM performance.

Table 6 Theory of mind and paranoid symptoms Persecutory and control groups

Task

ToM difficulty (in paranoid group compared with non-clinical controls)

Corcoran et al. (1995)

23 paranoid symptoms (delusions of reference or persecution or auditory hallucinations) 30 non-clinical controls 14 psychiatric controls 24 paranoid (delusions or reference, misidentification, and persecution with or without auditory hallucinations) 22 non-clinical controls 13 psychiatric control

Hinting task

✓

First and second order ToM tasks

✓

16 paranoid (delusions of reference, misidentification and/or persecution) 40 non-clinical controls 20 individuals with schizophrenia 20 non-clinical controls 28 schizophrenia 12 affective disorder 19 mild learning disability 18 schizophrenia and learning disability 20 non-clinical controls 21 persecutory delusions 12 depressed psychiatric control

Cartoon jokes requiring understanding of mental state Picture sequencing task

✓

18 individuals with schizophrenia 13 psychiatric controls

Irony task

Frith and Corcoran (1996)

Corcoran et al. (1997)

Langdon et al. (1997)

Doody et al. (1998)

Drury et al. (1998)

Mitchley et al.(1998)

First and second order ToM tasks

Correlation of ToM performance with paranoia or positive symptoms of psychosis within whole psychosis group

X

✓

A battery of ToM tasks including second order false belief tasks

X

Comments

The paranoid group performance was lower than the control group for both first order and second order ToM tasks. However when tests were made for matched IQ sub-groups the group difference was only significant for the second order tasks. It is also of note that the paranoid patients were finding the tasks simply more difficult as assessed by a memory question. The paranoid group was poorer than the control group for explaining jokes containing understanding of others' mental states, but did not statistically differ in explaining jokes with no theory of mind component. Poorer mentalising ability associated with negative symptoms. There was no association with paranoid symptoms. Performance on the second order ToM task was associated with the presence of positive and negative symptoms of psychosis.

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Study

This study did not include a non-clinical control group and therefore it cannot be determined whether the persecutory delusion group had ToM difficulties. However the individuals with persecutory delusions did not differ from the non-deluded depressed controls on any of the tasks. At a repeat assessment after symptom recovery the remitted delusion group had worse performance than the recovered depressed group on the second order false belief tasks. Poorer performance associated with negative and not positive symptoms of psychosis.

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Table 6 (continued ) Persecutory and control groups

Task

ToM difficulty (in paranoid group compared with non-clinical controls)

Correlation of ToM performance with paranoia or positive symptoms of psychosis within whole psychosis group

Comments

Pickup and Frith (2001)

16 paranoid 35 non-clinical controls

First and second order false belief tasks.

X

X

Mazza et al. (2001)

35 individuals with schizophrenia 25 Asperger syndrome

First and second order false beliefs tasks Projective imagination test

X

There were no differences for the first order tasks. On the second order task a statistical trend for the paranoid group to score lower than the controls was reported (p b .1) but this test was one-tailed, and since results in the opposite direction would not have been ignored, a two-tailed test would have been better to have reported and would have weakened the finding further. This trend disappeared with matching for IQ. In regression analyses negative symptoms and thought disorder were predictors of ToM performance. ToM performance was associated with negative symptoms and not positive symptoms of psychosis. Individuals with Asperger syndrome performed more poorly on the ToM task than the controls. Paranoia in the study participants was not associated with ToM scores. Paranoia was not associated with ToM performance. ToM performance was associated with the presence of negative symptoms (although this link was not significant when other neuropsychological task results were controlled for). ToM performance not associated with positive, negative, or disorganised symptoms, but with social functioning. In 22 individuals IQ was also assessed. When IQ was co-varied for in this sub-sample then poorer ToM performance was associated with the presence of positive symptoms. The delusion group performed poorer than the non-clinical controls on both tasks.

Blackshaw et al. (2001)

X

18 non-clinical controls Langdon et al. (2001)

32 individuals with psychosis 24 non-clinical controls

ToM picture sequencing task.

X

Roncone et al. (2002)

44 individuals with schizophrenia

First and second order ToM tasks

X

Randall et al. (2003)

15 persecutory delusions 15 remitted persecutory delusions group 14 non-clinical control

First and second order false belief tasks.

✓

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Study

42 people with schizophrenia (divided into a positive symptom group and a negative symptom group) 20 non-clinical controls

First and second order false belief tasks

X

Greig et al. (2004)

128 individuals with schizophrenia or schizo-affective disorder

Hinting task

X

Craig et al. (2004)

16 persecutory delusions 17 Asperger syndrome 16 non-clinical control

Hinting task and the ‘Reading the Mind in the Eyes’ task

Marjoram et al. (2005)

15 schizophrenia 15 affective (7 bipolar, 8 depression) 15 non-clinical controls

Hinting task.

✓

Kelemen et al. (2005)

52 individuals with schizophrenia 30 non-clinical controls 25 schizophrenia divided into persecutory delusions group and non-persecutory delusions group (13 and 12 respectively, McClure and Siegert, pers. com.). 38 non-clinical controls 19 persecutory delusions 15 non-persecutory delusion schizophrenia group (nine had no delusions) 21 non-clinical controls 61 individuals with schizophrenia (including 15 predominately paranoid symptoms) 22 non-clinical controls

Eyes test

X

Harrington et al. (2006)

Langdon et al. (2006)

Russell et al. (2006)

✓

1st and 2nd order verbal and non-verbal ToM tasks.

✓

False belief picture sequencing task

✓

Animations task

✓

✓

✓

From data presented, individuals with negative symptoms and individuals with positive symptoms perform poorer than the controls on the ToM tasks. Individuals with negative symptoms scored significantly lower than individuals with positive symptoms of psychosis. A non-clinical control group was not included in this study. Theory of mind performance was related to thought disorder in particular. ToM performance was also related to level of delusions, but not persecutory delusions. Both the delusions group and the Asperger group performed more poorly than the controls on the tasks. Higher levels of paranoia were associated with poorer ToM performance. Participants with delusions and hallucinations performed significantly lower than the control group. However it is unclear whether this is due to the presence of persecutory delusions. There was also a trend for negative symptoms to be associated with poorer ToM performance. ToM performance correlated with negative but not positive symptoms of psychosis. Persecutory delusions associated with ToM performance. Differences on verbal tasks. Also an association of ToM performance with formal thought disorder.

Both clinical groups performed more poorly than the control group.

X

A novel ToM task was used in this study, requiring judges to rate the participants' responses.

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Mazza, De Risio, Surian, Roncone, and Casacchia (2001)

ToM performance was not associated with negative or positive symptoms of psychosis.

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Greig et al. (2004) and Harrington et al. (2006) note that mixed findings might relate to the different ToM tasks used in studies, the different symptom groupings in studies, small sample sizes, and the idea that ToM may not be the only factor contributing to persecutory experience. These issues do complicate the findings. However, the literature is beginning to indicate that although ToM problems may be present in people with persecutory delusions they are certainly not specific or necessary to this experience and their presence in people with paranoid experiences may actually be due to the presence of negative symptoms and thought disorder (conceptual disorganisation and psychomotor poverty syndromes). Difficulties with theory of mind abilities may not be central to the development of persecutory ideation. Walston et al.'s (2000) finding of intact ToM in individuals with pure persecutory delusions is very much consistent with such a view. Like the attribution work, a large early episode study is required, combining good ToM assessment and measures of different positive and negative symptoms and controlling for different positive and negative symptoms, IQ, executive functioning and social functioning. ToM abilities have not been fully examined in relation to dimensional measures of delusional ideation or paranoia. Such studies seem warranted and could provide good dimensional tests of symptom associations with ToM performance. Only Langdon and Coltheart (2004a, 2004b) have taken this approach. In a small student samples higher levels of schizotypy were found to be associated with lower mentalising abilities, but no consistent pattern with different schizotypy factors and ToM was found. A very interesting study by McCabe, Heath, Burns, and Priebe (2002) merits note. They argue that if ToM difficulties are present then they should be detectable in real-life social interactions. These researchers found that outpatients with positive and negative symptoms of schizophrenia actually showed intact ToM skills in conversations with mental health professions. The patients represented mental states of others coherently and used them effectively. Furthermore, some patients knew that others did not share their delusions and viewed their beliefs as odd, and examples are given of patients understanding implicit messages in therapists' speech. McCabe notes that some problems of communication were apparent in the conversations but not those expected from ToM accounts. The theoretical account of how ToM relates to paranoid experiences contains weaknesses. While this work has developed from the plausible argument that by definition persecutory delusions reflect incorrect judgements of the intentions of others, the ToM account of schizophrenia is much weaker in explaining exactly why a mentalising problem should lead to paranoid thoughts. It does not seem inevitable that difficulties in reading others' intentions would lead to the explanation that people are disguising their intentions and forming a conspiracy. Many paranoid individuals would say that their persecutors are not disguising their intentions and indeed make their intent all too clear. Furthermore, Walston et al. (2000) make the point that if everybody's mental states are opaque persecutory delusions should not be restricted to a single person or group as is often the case. In short, a mentalising difficulty may lead to incorrect inferences but why errors that are paranoid and often circumscribed? 8. The threat anticipation cognitive model of persecutory delusions Conceptualising delusions as beliefs has provided the main theoretical opening for psychological research. As McReynolds (1960) notes: ‘It appears that delusional beliefs are not formally different from non-delusional beliefs.’ Maher has highlighted that the beliefs result from trying to make sense of events, especially anomalous experiences that invite explanation. It is likely that the delusional explanations and their persistence are closely tied to reasoning processes. For persecutory thinking in particular, consideration of the phenomenology has identified anxiety as a key contributory factor. These principal findings have been integrated into the threat anticipation model of paranoia (Freeman & Garety, 2004; Freeman et al., 2002, 2006). The model is explicitly built on the idea that there are multiple factors responsible for the development and maintenance of paranoia. Furthermore, the model addresses the multidimensional nature of persecutory experience, highlighting specific factors for the development of delusion content, conviction, persistence, and distress (Figs. 2 and 3). Following the influential work of Maher (1974), delusional beliefs are considered as explanations of experience. The sorts of experiences considered as the proximal source of evidence for persecutory delusions are: • Internal feelings. Unusual or anomalous experiences are frequently key to delusional ideation. These include: being in a heightened state/aroused; having feelings of significance; perceptual anomalies (e.g. things may seem vivid or bright or piercing, sounds may feel very intrusive); having feelings as if one is not really there (depersonalisation); and illusions and hallucinations (e.g. hearing voices). These sorts of experiences can be caused by the processes hypothesised by theorists such as Hemsely (1994) and Frith (1992), by the use of street drugs or by high levels of affect.

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Fig. 2. Summary of the formation of a persecutory delusion.

• External events. Ambiguous social information is particularly important. This includes both non-verbal information (e.g. facial expressions, people's eyes, hand gestures, laughter/smiling) and verbal information (e.g. snatches of conversation, shouting). Coincidences and negative or irritating events also feature in persecutory ideation. Typically, individuals vulnerable to paranoid thinking try to make sense of internal unusual experiences by drawing in negative, discrepant, or ambiguous external information. For example, a person may go outside feeling in an unusual state and, rather than label this experience as such (e.g. ‘I'm feeling a little odd and anxious today, probably because I've not been sleeping well’), the feelings are instead used as a source of evidence, together with the facial expressions of strangers in the street, that there is a threat (e.g. ‘People don't like me and may harm me’). Persecutory delusions are viewed as explanations that contain threat beliefs about physical, social, or psychological harm. But why a suspicious interpretation of experiences? The internal and external events are interpreted in line with previous experiences, knowledge, emotional state, memories, personality, and decision-making processes and therefore the origin of persecutory explanations lies in such psychological processes. Suspicious thoughts often occur in the context of emotional distress. They are frequently preceded by stressful events (e.g. difficult interpersonal relationships, bullying, isolation). Furthermore, the stresses may happen against a background of previous experiences that have led the person to have beliefs about the self (e.g. as vulnerable), others (e.g. as potentially dangerous), and the world (e.g. as bad) that make suspicious thoughts more likely to occur. Living in difficult urban areas is likely to increase the accessibility of such negative views about others. These sorts of negative beliefs about the self and others are associated with anxiety and depression, but anxiety may be especially important in the generation of persecutory ideation. The theme of anxiety is the anticipation of danger and it is the origin of the threat content in persecutory ideation. Anxiety may be fleeting in the

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Fig. 3. Summary of the maintenance of a persecutory delusion.

generation of a paranoid thought, but paranoid thoughts will be more significant in the context of higher levels of trait anxiety. Paranoid thoughts are hypothesised to have close links with anxiety processes. Worry may keep the suspicions in mind and develop the content in a catastrophising manner. Hence in the model emotion is given a direct role in delusion formation. The anxious thoughts are hypothesised to become truly persecutory when an attribution is made concerning the intention of the perpetrators. The cause of this idea of intent is under-researched. Most often the threat beliefs contain an implicit attribution of intent. In other cases anger – often not expressed because of fear of others' reactions – may contribute to this attribution of hostile intent, since judgements of blame and attributions of intent are central to anger. The persecutory ideas are most likely to become of a delusional intensity when there are accompanying biases in reasoning such as reduced data gathering (‘jumping to conclusions’) (Garety & Freeman, 1999), a failure to generate or consider alternative explanations for experiences (Freeman et al., 2004), and a strong confirmatory reasoning bias (Freeman, Garety, Kuipers, & McGuire, 2005). Social isolation may also contribute to a failure to fully review paranoid thoughts. When reasoning biases are present, the suspicions are more likely to become near certainties; the threat beliefs become held with a conviction unwarranted by the evidence and may then be considered delusional. In the model there are further hypotheses concerning the maintenance of persecutory delusions and the associated emotional reaction. For example, since the explanations are threat beliefs they will be maintained by processes that maintain anxiety disorders, such as self-focus and safety behaviours (see Clark, 1999). Distress is hypothesised to arise from two processes: aspects of the content of the delusion (e.g. beliefs about the power of the persecutor, control over the

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threat, deservedness of harm) and further appraisal of the experience (e.g. worry and rumination). Beyond the defining ideas of threat and attribution of intent, the content of paranoia varies in the individual case, particularly important being affect-laden beliefs that vary dimensionally (Freeman et al., 2001). For example, beliefs about the degree to which harm is deserved are viewed as one aspect of the content of the delusion important in determining the level of distress, but not indicating the presence of a discrete type of paranoia. More broadly, it is of interest to note that reactions to delusions, such as worrying, are not considered the only route to distress and the development of clinical cases — specific aspects of the content of beliefs make distress more likely too. Thus, emphasised in the psychological understanding of persecutory ideation are: anomalous experiences, such as hallucinations, which may be caused by core cognitive dysfunction and street drug use; affective processes, especially anxiety, worry, and interpersonal sensitivity; reasoning biases, particularly belief confirmation, jumping to conclusions, and belief inflexibility; and social factors, such as isolation and trauma. 9. Pitfalls in studying persecutory thinking Developments in the understanding of paranoia have been heralded, but recognition and discussion of the methodologies and pitfalls of researching paranoia have been lacking. In this review the tendency to ignore the multidimensional nature of the experience and the failure to define the phenomena of interest in detail have been highlighted. Two other important issues bear upon research on delusions: the recruitment of participants and the course of illness. Research on delusions is likely to have been affected by systematic recruitment biases. For instance, individuals with persecutory delusions that are the most strongly held, preoccupying, and distressing are probably the least likely to participate. Conversely, it is easier to recruit a patient into a research study as their paranoia diminishes. For purposes of comparison across studies, it would be helpful if researchers report the levels of belief conviction, preoccupation, and distress of the participants. In addition, data on levels of emotional disorder are informative. Recruitment of participants is also often ad hoc and it is often not clear whether all suitable individuals within a referral system have been approached. Even then it is common for half of patients who meet study criteria to refuse to participate. The demands of each research study will also affect patient recruitment. How representative a study group is, and the potential influence on study results of recruitment biases, needs to be given greater attention. Course of illness (history length and symptom outcome) are also likely to relate to recruitment biases, and may have importance in the interpretation of results. Individuals at first episode may be more difficult to recruit into research, in comparison with people with multiple episodes, because they are currently coming to terms with their experiences. Moreover, individuals who have symptoms that quickly and fully recover often do not attend services, particularly if they do not relapse, and therefore they seldom participate in research studies. There may be differences in participation rates depending upon recovery styles such as ‘sealing over’ or ‘integration’ (McGlashan, Levy, & Carpenter, 1975). There are theoretical reasons why it is likely that the course of illness may affect the results of studies. The presentation of individuals after their initial episode will be affected by this first experience of symptoms and psychiatric services, particularly in relation to emotion. Depression and self blame may become more prominent and emotions such as anger, which may have been important at delusion formation, may recede. This may particularly be the case in instances when there has been a long chronic course in which symptoms have never fully remitted. It is also likely that the factors that trigger relapses may be different from those at first episode (e.g. the fear of relapse itself). The difficulties in recruiting participants whose symptoms quickly remit will limit what can be learnt about the factors that promote recovery. Clearly, cross-sectional studies that include both individuals with symptoms that recover and individuals whose symptoms tend to persist will make it more difficult to detect maintenance processes if the variable of recovery is not included in the analysis (a failing of previous studies); however, longitudinal studies are generally preferable, but these are few in number (Startup et al., in press). 10. The next 10 years and beyond In this review a number of factors have been highlighted as important to the development of persecutory delusions. However, studies have mainly concerned associations of psychological factors and persecutory thinking. It is now time for the causal roles of these variables to be investigated, for example in experimental manipulation studies (e.g. examining the effects of reducing or increasing anxiety). There is a need to have more longitudinal studies of natural recovery. Furthermore, psychological factors need to be studied together, including testing for interactions between variables (e.g. anxiety and the presence of anomalous experience). It is important to note that studies of delusional ideation dimensionally in the general population enable recruitment of a larger number of participants than are possible for studies of clinical

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populations and therefore provides a better means of testing complex models. In order for such work, however, to be considered convincing for the psychosis field, it needs to be carried out in the context of detailed scrutiny of both the similarities and differences between clinical cases of persecutory delusions, non-clinical cases of persecutory delusions, and non-clinical paranoid ideation. Aside from psychological factors, which have been the focus of the review, there is considerable work needed on the phenomenological examination of persecutory ideation. As distress is often what marks out clinical from non-clinical cases, an understanding of its causes should be a higher priority, and content of the beliefs is one cause of distress. One future line of clinically relevant research would be the investigation of change in delusion content. How do the important emotional content and associated appraisals in delusional systems change with recovery? How do the internal contents of a delusion change in relation to each other? This type of approach has the potential to form a link with patient views of recovery. Furthermore, persecutory thinking can be associated with other delusion sub-types, particularly reference but also sometimes grandiose, and the inter-relationships between symptoms need to be considered. For example, persecutory thinking often builds upon ideas of reference. But it is also the case that it will be important to identify the factors that distinguish, for example, paranoid from grandiose thinking or anxious thinking. From the review, ten research questions for future investigation are apparent: 1. Can psychological models of paranoia be shown to have high accuracy in explaining the occurrence of persecutory thoughts? 2. How do psychological factors relate to the different dimensions of delusional experience? 3. What are the psychological factors that distinguish clinical from non-clinical paranoia? 4. Can it be shown that psychological factors are causal in paranoid thinking? 5. Do psychological factors interact in the development of paranoia? 6. What factors distinguish the development of persecutory ideation from the development of grandiosity? 7. What distinguishes the development of paranoid from anxious fears? 8. What are the key emotion-associated aspects of paranoid thoughts and how do they change with time? 9. How do psychological processes relate to social and biological factors potentially associated with paranoia? 10. Can the developments in the understanding of paranoia be used to improve treatments? In the past, paranoia was too often studied only in the context of severe mental illness and, even then, researchers were trying to explain a diagnosis such as schizophrenia rather than persecutory thinking itself. Researchers over the last 10 years have begun to free paranoia from this association, and view it as a phenomenon to be explained in its own right, linking it with suspicious thoughts apparent in many people in the general population. Moreover, analogies with the study of depressive and anxious thinking are being made. The key questions for the future study of persecutory thinking are now becoming apparent and over the next 10 years there are likely to be great strides in understanding in this important clinical area as it receives greater attention. These developments in understanding will then need to be translated into improvements in the emerging cognitive–behavioural treatments for paranoid thoughts (Freeman et al., 2006). Acknowledgement Daniel Freeman is supported by a Wellcome Trust Fellowship. References Allen, P., Freeman, D., Johns, L., & McGuire, P. (2006). Misattribution of self-generated speech in relation to hallucinatory proneness and delusional ideation in healthy volunteers. Schizophrenia Research, 84, 281−288. American Psychiatric Association (1994). Diagnostic and statistical manual of mental disorders, Fourth Ed. Washington, DC: American Psychiatric Association. Äsberg, M., Montgomery, S. A., Perris, C., Schalling, D., & Sedvall, G. (1978). A comprehensive psychopathological rating scale. Acta Psychiatrica Scandinavica, 271, 5−27. Bacon, F. (1612). The essaies of Sr. Francis Bacon Knight, the Kings Solliciter Generall. London: John Beale. Barrowclough, C., Tarrier, N., Humphreys, L., Ward, J., Gregg, L., & Andrews, B. (2003). Self-esteem in schizophrenia: Relationships between selfevaluation, family attitudes, and symptomatology. Journal of Abnormal Psychology, 112, 92−99. Bebbington, P. E., & Nayani, T. (1995). The Psychosis Screening Questionnaire. International Journal of Methods in Psychiatric Research, 5, 11−19.

D. Freeman / Clinical Psychology Review 27 (2007) 425–457

453

Bell, V., Halligan, P. W., & Ellis, H. D. (2006). The Cardiff Anomalous Perceptions Scale (CAPS). Schizophrenia Bulletin, 32, 366−377. Bentall, R. P. (1990). The syndromes and symptoms of psychosis. Or why you can't play ‘twenty questions’ with the concept of schizophrenia and hope to win. In R. P. Bentall (Ed.), Reconstructing schizophrenia (pp. 23−60). London: Routledge. Bentall, R. P., Corcoran, R., Howard, R., Blackwood, N., & Kinderman, P. (2001). Persecutory delusions: A review and theoretical interpretation. Clinical Psychology Review, 21, 1143−1192. Bentall, R. P., & Kaney, S. (1989). Content specific processing and persecutory delusions: An investigation using the emotional Stroop test. British Journal of Medical Psychology, 62, 355−364. Bentall, R. P., Kinderman, P., & Kaney, S. (1994). The self, attributional processes and abnormal beliefs: Towards a model of persecutory delusions. Behaviour Research and Therapy, 32, 331−341. Birchwood, M. (2003). Pathways to emotional dysfunction in first episode psychosis. British Journal of Psychiatry, 182, 373−375. Birchwood, M., Meaden, A., Trower, P., Gilbert, P., & Plaistow, J. (2000). The power and omnipotence of voices: Subordination and entrapment by voices and significant others. Psychological Medicine, 30, 337−344. Birchwood, M., & Trower, P. (2006). The future of cognitive–behavioural therapy for psychosis: Not a quasi-neuroleptic. British Journal of Psychiatry, 188, 107−108. Blackshaw, A. J., Kinderman, P., Hare, D. J., & Hatton, C. (2001). Theory of mind, causal attribution and paranoia in Asperger syndrome. Autism, 5, 147−163. Boyd, T., & Gumley, A. (in press). An experiential perspective on persecutory paranoia. Psychology and Psychotherapy. Broome, M. R., Johns, L. C., Valli, I., Woolley, J. B., Tabraham, P., Brett, C., Valmaggia, L., Peters, E., Garety, P. A., & McGuire, P. K. (in press). People with an At Risk Mental State jump to conclusions. British Journal of Psychiatry. Brüne, M. (2005). “Theory of mind” in schizophrenia. Schizophrenia Bulletin, 31, 21−42. Buchanan, A., Reed, A., Wessely, S., Garety, P., Taylor, P., Grubin, D., & Dunn, G. (1993). Acting on delusions. II: The phenomenological correlates of acting on delusions. British Journal of Psychiatry, 163, 77−81. Bunney, W. E., Hetrick, W. P., Bunney, B. G., Patterson, J. V., Jin, Y., Potkin, S. G., et al. (1999). Structured interview for assessing perceptual anomalies (SIAPA). Schizophrenia Bulletin, 25, 577−592. Butler, R. W., Mueser, K. T., Sprock, J., & Braff, D. L. (1996). Positive symptoms of psychosis in posttraumatic stress disorder. Biological Psychiatry, 39, 839−844. Cameron, N. (1959). The paranoid pseudo-community revisited. American Journal of Sociology, 65, 52−58. Candido, C. L., & Romney, D. M. (1990). Attributional style in paranoid versus depressed patients. British Journal of Medical Psychology, 63, 355−363. Chadwick, P. D. J., Trower, P., Juusti-Butler, T. -M., & Maguire, N. (2005). Phenomenological evidence for two types of paranoia. Psychopathology, 38, 327−333. Chapman, L. J., & Chapman, J. P. (1980). Scales for rating psychotic and psychotic-like experiences as continua. Schizophrenia Bulletin, 6, 476−489. Chapman, L. J., Chapman, J. P., Kwapil, T. R., Eckbald, M., & Zinser, M. C. (1994). Putatively psychosis-prone subjects 10 years later. Journal of Abnormal Psychology, 103, 171−183. Chapman, R. K. (2002). First person account: Eliminating delusions. Schizophrenia Bulletin, 28, 545−553. Chisholm, B., Freeman, D., & Cooke, A. (2006). Identifying potential predictors of PTSD reactions to psychotic episodes. British Journal of Clinical Psychology, 45, 545−559. Christenson, R., & Blazer, D. (1984). Epidemiology of persecutory ideation in an elderly population in the community. American Journal of Psychiatry, 141, 1088−1091. Claridge, G. (1994). Single indicators of risk for schizophrenia. Probably fact or likely myth? Schizophrenia Bulletin, 20, 151−168. Claridge, G. (1997). Schizotypy: Implications for illness and health. Oxford: Oxford University Press. Clark, D. M. (1999). Anxiety disorders: Why they persist and how to treat them. Behaviour Research and Therapy, 37, S5−S27. Cohen, C. I., Magai, C., Yaffee, R., & Walcott-Brown, L. (2004). Racial differences in paranoid ideation and psychoses in an older urban population. American Journal of Psychiatry, 161, 864−871. Colbert, S. M., & Peters, E. R. (2002). Need for closure and jumping-to-conclusions in delusion-prone individuals. Journal of Nervous and Mental Disease, 170, 27−31. Conway, C. R., Bollini, A. M., Graham, B. G., Keefe, R. S. E., Schiffman, S. S., & McEvoy, J. P. (2002). Sensory acuity and reasoning in delusional disorder. Comprehensive Psychiatry, 43, 75−178. Cooper, A. F., & Curry, A. R. (1976). The pathology of deafness in the paranoid and affective psychoses of later life. Journal of Psychosomatic Research, 20, 97−105. Corcoran, R., Cahill, C., & Frith, C. D. (1997). The appreciation of visual jokes in people with schizophrenia. Schizophrenia Research, 24, 319−327. Corcoran, R., Mercer, G., & Frith, C. D. (1995). Schizophrenia, symptomology and social inference. Schizophrenia Research, 17, 5−13. Craig, J. S., Hatton, C., Craig, F. B., & Bentall, R. P. (2004). Persecutory beliefs, attributions and theory of mind. Schizophrenia Research, 69, 29−33. Delespaul, P. (1995). Assessing schizophrenia in daily life. Maastricht: Maastricht University Press. Derogatis, L. R., Lipman, R. S., & Covi, L. (1973). SCL-90: An outpatient psychiatric rating scale—preliminary report. Psychopharmacological Bulletin, 9, 13−28. Docherty, J. P., Van Kammen, D. P., Siris, S. G., & Marder, S. R. (1978). Stages of onset of schizophrenic psychosis. American Journal of Psychiatry, 135, 420−426. Doody, G. A., Götz, M., Johnstone, E. C., Frith, C. D., & Cunningham Owens, D. G. (1998). Theory of mind and psychoses. Psychological Medicine, 28, 397−405. Drake, R. J., Pickles, A., Bentall, R. P., Kinderman, P., Haddock, G., Tarrier, N., et al. (2004). The evolution of insight, paranoia and depression during early schizophrenia. Psychological Medicine, 34, 285−292.

454

D. Freeman / Clinical Psychology Review 27 (2007) 425–457

Drury, V. M., Robinson, E. J., & Birchwood, M. (1998). ‘Theory of mind’ skills during an acute episode of psychosis and following recovery. Psychological Medicine, 28, 1101−1112. D'Souza, D. C., Perry, E., MacDougall, L., Ammerman, Y., Cooper, T., Wu, Y., et al. (2004). The psychotomimetic effects of intravenous delta 9-tetrahydrocannabinol in healthy individuals: Implications for psychosis. Neuropsychopharmacology, 29, 1558−1572. Dudley, R. E. J., John, C. H., Young, A. W., & Over, D. E. (1997a). Normal and abnormal reasoning in people with delusions. British Journal of Clinical Psychology, 36, 243−258. Dudley, R. E. J., John, C. H., Young, A. W., & Over, D. E. (1997b). The effect of self-referent material on the reasoning of people with delusions. British Journal of Clinical Psychology, 36, 575−584. Dudley, R. E. J., & Over, D. E. (2003). People with delusions jump to conclusions. Clinical Psychology and Psychotherapy, 10, 263−274. Eaton, W. W., Romanoski, A., Anthony, J. C., & Nestadt, G. (1991). Screening for psychosis in the general population with a self-report interview. Journal of Nervous and Mental Disease, 179, 689−693. Ellett, L., Lopes, B., & Chadwick, P. (2003). Paranoia in a non-clinical population of college students. Journal of Nervous and Mental Disease, 191, 425−430. Eysenck, M. W., & Van Berkum, J. (1992). Trait anxiety, defensiveness, and the structure of worry. Personality and Individual Differences, 13, 1285−1290. Fear, C. F., & Healy, D. (1997). Probabilistic reasoning in obsessive-compulsive and delusional disorders. Psychological Medicine, 27, 199−208. Fear, C., Sharp, H., & Healy, D. (1996). Cognitive processes in delusional disorders. British Journal of Psychiatry, 168, 1−8. Flint, A. J. (1991). Delusions in dementia: A review. Journal of Neuropsychiatry and Clinical Neurosciences, 3, 121−130. Fornells-Ambrojo, M., & Garety, P. A. (2005). Bad me paranoia in early psychosis: A relatively rare phenomenon. British Journal of Clinical Psychology, 44, 521−528. Forsell, Y., & Henderson, A. S. (1998). Epidemiology of paranoid symptoms in an elderly population. British Journal of Psychiatry, 172, 429−432. Fowler, D. (2000). Psychological formulation of early episodes of psychosis: A cognitive model. In M. Birchwood, D. Fowler, & C. Jackson (Eds.), Early intervention in psychosis: A guide to concepts, evidence and interventions (pp. 101−127). Chichester: Wiley. Fowler, D., Freeman, D., Smith, B., Kuipers, E., Bebbington, P., Bashforth, H., et al. (2006). The Brief Core Schema Scales (BCSS): Psychometric properties and associations with paranoia and grandiosity in non-clinical and psychosis samples. Psychological Medicine, 36, 749−759. Frangos, E., Athanassenas, G., Tsitourides, S., Psilolignos, P., & Katsanou, N. (1983). Psychotic depressive disorder. A separate entity? Journal of Affective Disorders, 5, 259−265. Freeman, D. (2006). Delusions in the non-clinical population. Current Psychiatry Reports, 8, 191−204. Freeman, D., Dunn, G., Garety, P. A., Bebbington, P., Slater, M., Kuipers, E., et al. (2005a). The psychology of persecutory ideation I: A questionnaire study. Journal of Nervous and Mental Disease, 193, 302−308. Freeman, D., Freeman, J., & Garety, P. (2006). Overcoming paranoid and suspicious thoughts. London: Robinson Constable. Freeman, D., & Garety, P. A. (1999). Worry, worry processes and dimensions of delusions: An exploratory investigation of a role for anxiety processes in the maintenance of delusional distress. Behavioural and Cognitive Psychotherapy, 27, 47−62. Freeman, D., & Garety, P. A. (2000). Comments on the content of persecutory delusions: Does the definition need clarification? British Journal of Clinical Psychology, 39, 407−414. Freeman, D., & Garety, P. A. (2003). Connecting neurosis and psychosis: The direct influence of emotion on delusions and hallucinations. Behaviour Research and Therapy, 41, 923−947. Freeman, D., & Garety, P. A. (2004). Paranoia: The Psychology of Persecutory Delusions. Hove: Psychology Press. Freeman, D., Garety, P. A., Bebbington, P., Slater, M., Kuipers, E., Fowler, D., et al. (2005b). The psychology of persecutory ideation II: A virtual reality experimental study. Journal of Nervous and Mental Disease, 193, 309−315. Freeman, D., Garety, P. A., Bebbington, P. E., Smith, B., Rollinson, R., Fowler, D., et al. (2005c). Psychological investigation of the structure of paranoia in a non-clinical population. British Journal of Psychiatry, 186, 427−435. Freeman, D., Garety, P. A., Fowler, D., Kuipers, E., Bebbington, P., & Dunn, G. (2004). Why do people with delusions fail to choose more realistic explanations for their experiences? An empirical investigation. Journal of Consulting and Clinical Psychology, 72, 671−680. Freeman, D., Garety, P., Fowler, D., Kuipers, E., Dunn, G., Bebbington, P., et al. (1998). The London–East Anglia randomised controlled trial of cognitive behaviour therapy for psychosis IV: Self-esteem and persecutory delusions. British Journal of Clinical Psychology, 37, 415−430. Freeman, D., Garety, P. A., & Kuipers, E. (2001). Persecutory delusions: Developing the understanding of belief maintenance and emotional distress. Psychological Medicine, 31, 1293−1306. Freeman, D., Garety, P. A., Kuipers, E., Colbert, S., Jolley, S., Fowler, D., et al. (2006). Delusions and decision-making style: Use of the Need for Closure Scale. Behaviour Research and Therapy, 44, 1147−1158. Freeman, D., Garety, P. A., Kuipers, E., Fowler, D., & Bebbington, P. E. (2002). A cognitive model of persecutory delusions. British Journal of Clinical Psychology, 41, 331−347. Freeman, D., Garety, P., Kuipers, E., Fowler, D., Bebbington, P. E., & Dunn, G. (2007). Acting on persecutory delusions: The importance of safety seeking. Behaviour Research and Therapy, 45, 89−99. Freeman, D., Garety, P. A., McGuire, P., & Kuipers, E. (2005). Developing a theoretical understanding of therapy techniques: Reasoning, therapy and symptoms. British Journal of Clinical Psychology, 44, 241−254. Freeman, D., Slater, M., Bebbington, P. E., Garety, P. A., Kuipers, E., Fowler, D., et al. (2003). Can virtual reality be used to investigate persecutory ideation? Journal of Nervous and Mental Disease, 191, 509−514. Frith, C. D. (2004). Schizophrenia and theory of mind. Psychological Medicine, 34, 385−389. Frith, C. D. (1992). The cognitive neuropsychology of schizophrenia. Hove: LEA. Frith, C. D., & Corcoran, R. (1996). Exploring ‘theory of mind’ in people with schizophrenia. Psychological Medicine, 26, 521−530.

D. Freeman / Clinical Psychology Review 27 (2007) 425–457

455

Garety, P. A., & Freeman, D. (1999). Cognitive approaches to delusions: A critical review of theories and evidence. British Journal of Clinical Psychology, 38, 113−154. Garety, P. A., Freeman, D., Jolley, S., Dunn, G., Bebbington, P. E., & Fowler, D. (2005). Reasoning, emotions and delusional conviction in psychosis. Journal of Abnormal Psychology, 114, 373−384. Garety, P. A., & Hemsley, D. R. (1994). Delusions: Investigations into the psychology of delusional reasoning. Oxford: Oxford University Press. Garety, P. A., Hemsley, D. R., & Wessely, S. (1991). Reasoning in deluded schizophrenic and paranoid patients: Biases in performance on a probabilistic inference task. Journal of Nervous and Mental Disorder, 179, 194−201. Garety, P. A., Kuipers, E., Fowler, D., Freeman, D., & Bebbington, P. E. (2001). A cognitive model of the positive symptoms of psychosis. Psychological Medicine, 31, 189−195. Gilbert, P., Boxall, M., Cheung, M., & Irons, C. (2005). The relation of paranoid ideation and social anxiety in a mixed clinical population. Clinical Psychology and Psychotherapy, 12, 124−133. Goodwin, F., & Jamison, K. (1990). Manic-depressive illness. Oxford: Oxford University Press. Green, C., Garety, P. A., Freeman, D., Fowler, D., Bebbington, P. E., Dunn, G., et al. (2006). Phenomenology and affect in persecutory delusions. British Journal of Clinical Psychology, 45, 561−577. Greig, T. C., Bryson, G. J., & Bell, M. D. (2004). Theory of mind performance in schizophrenia. Journal of Nervous and Mental Disease, 192, 12−18. Guillem, F., Pampoulova, T., Stip, E., Lalonde, P., & Todorov, C. (2005). The relationships between symptom dimensions and dysphoria in schizophrenia. Schizophrenia Research, 75, 83−96. Hamner, M. B., Freuch, C. B., Ulmer, H. G., & Arana, G. W. (1999). Psychotic features and illness severity in combat veterans with chronic posttraumatic stress disorder. Biological Psychiatry, 45, 846−852. Harrington, L., Langdon, R., Seigert, R. J., & McClure, J. (2005). Schizophrenia, theory of mind, and persecutory delusions. Cognitive Neuropsychiatry, 10, 87−104. Harrington, L., Siegert, R. J., & McClure, J. (2005). Theory of mind in schizophrenia. Cognitive Neuropsychiatry, 10, 249−286. Hemsley, D. R. (1994). Perceptual and cognitive abnormalities as the bases for schizophrenic symptoms. In A. S. David & J.C. Cutting (Eds.), The neuropsychology of schizophrenia (pp. 97−116). Hove: Erlbaum. Hughes, C. (2002). Executive functions and development: Emerging themes. Infant and Child Psychology, 11, 201−209. Huppert, J. D., & Smith, T. E. (2005). Anxiety and schizophrenia; the interaction of subtypes of anxiety and psychotic symptoms. CNS Spectrums, 10, 72−731. Huq, S. F., Garety, P. A., & Hemsley, D. R. (1988). Probabilistic judgements in deluded and non-deluded subjects. Quarterly Journal of Experimental Psychology, 40A, 801−812. Janssen, I., Krabbendam, L., Jolles, J., & van Os, J. (2003). Alterations in theory of mind in patients with schizophrenia and non-psychotic relatives. Acta Psychiatrica Scandinavica, 108, 110−117. Johns, L. C. (2005). Hallucinations in the general population. Current Psychiatry Reports, 7, 162−167. Johns, L. C., Cannon, M., Singleton, N., Murray, R. M., Farrell, M., Brugha, T., et al. (2004). The prevalence and correlates of self-reported psychotic symptoms in the British population. British Journal of Psychiatry, 185, 298−305. Johns, L. C., Gregg, L., Allen, P., & McGuire, P. K. (2006). Impaired verbal self-monitoring in psychosis. Psychological Medicine, 36, 465−474. Johnson, J., Horwath, E., & Weissman, M. M. (1991). The validity of major depression with psychotic features based on a community sample. Archives of General Psychiatry, 48, 1075−1081. Jolley, S., Garety, P. A., Bebbington, P. E., Dunn, G., Freeman, D., Kuipers, E., et al. (2006). Attributional style in psychosis—the role of affect and belief type. Behaviour Research and Therapy, 44, 1597−1607. Kapur, S. (2003). Psychosis as a state of aberrant salience: A framework linking biology, phenomenology, and pharmacology. American Journal of Psychiatry, 160, 13−23. Kelemen, O., Erdélyi, R., Pataki, I., Benedek, G., Janka, Z., & Kéri, S. (2005). Theory of mind and motion perception in schizophrenia. Neuropsychology, 19, 494−500. Kincannon, J. C. (1968). Predictions of the standard MMPI scale scores from 71 items: The Mini-mult. Journal of Consulting and Clinical Psychology, 32, 319−325. Kinderman, P., & Bentall, R. P. (1996a). A new measure of causal locus: The internal, personal and situational attributions questionnaire. Personality and Individual Differences, 20, 261−264. Kinderman, P., & Bentall, R. P. (1996b). Self-discrepancies and persecutory delusions. Journal of Abnormal Psychology, 105, 106−113. Kinderman, P., Kaney, S., Morley, S., & Bentall, R. P. (1992). Paranoia and the defensive attributional style. British Journal of Medical Psychology, 65, 371−383. Krabbendam, L., Janssen, I., Bijl, R. V., Vollebergh, W. A. M., & van Os, J. (2002). Neuroticism and low self-esteem as risk factors for psychosis. Social Psychiatry and Psychiatric Epidemiology, 37, 1−6. Krabbendam, L., Myin-Germeys, I., Hanssen, M., Bijil, R. V., de Graaf, R., Vollebergh, W., et al. (2004). Hallucinatory experiences and onset of psychotic disorder: Evidence that the risk is mediated by delusion formation. Acta Psychiatrica Scandinavica, 110, 264−272. Kraepelin, E. (1921). Manic-depressive insanity and paranoia. Edinburgh: Livingstone. Kripke, S. (1980). Naming and necessity. Oxford: Blackwell. Krstev, H., Jackson, H., & Maude, D. (1999). An investigation of attributional style in first-episode psychosis. British Journal of Clinical Psychology, 38, 181−194. Langdon, R., & Coltheart, M. (2004). Recognition of metaphor and irony in young adults. Psychiatry Research, 125, 9−20. Langdon, R., & Coltheart, M. (2004). Mentalising, schizotypy, and schizophrenia. Cognition, 71, 43−71. Langdon, R., Coltheart, M., Ward, P. B., & Catts, S. V. (2001). Mentalising, executive planning and disengagement in schizophrenia. Cognitive Neuropsychiatry, 6, 81−108.

456

D. Freeman / Clinical Psychology Review 27 (2007) 425–457

Langdon, R., Corner, T., McLaren, J., Ward, P. B., & Coltheart, M. (2006). Externalising and personalising biases in persecutory delusions. Behaviour Research and Therapy, 44, 699−713. Langdon, R., Michie, P. T., Ward, P. B., McConaghy, N., Catts, S. V., & Coltheart, M. (1997). Defective self and/or other mentalising in schizophrenia. Cognitive Neuropsychiatry, 2, 167−193. Lyon, H. M., Kaney, S., & Bentall, R. P. (1994). The defensive function of persecutory delusions: Evidence from attribution tasks. British Journal of Psychiatry, 164, 637−646. Maher, B. A. (1974). Delusional thinking and perceptual disorder. Journal of Individual Psychology, 30, 98−113. Maher, B. A. (1988). Anomalous experience and delusional thinking: The logic of explanations. In T. F. Oltmanns & B. A. Maher (Eds.), Delusional beliefs (pp. 15−33). New York: Wiley. Maher, B. A. (2003). Psychopathology and delusions: Reflections on methods and models. In M. F. Lenzenweger & J. M. Hooley (Eds.), Principles of experimental psychopathology: Essays in honor of Brendan A. Maher (pp. 9−28). Washington: American Psychological Association. Maric, N., Myin-Germeys, I., Delespaul, P., de Graaf, R., Vollebergh, W., & van Os, J. (2004). Is our concept of schizophrenia influenced by Berkson's bias? Social Psychiatry and Psychiatric Epidemiology, 39, 600−605. Marjoram, D., Gardner, C., Burns, J., Miller, P., Lawrie, S. M., & Johnstone, E. C. (2005). Symptomatology and social inference. Cognitive Neuropsychiatry, 10, 347−359. Martin, J. A., & Penn, D. L. (2001). Brief report: Social cognition and subclinical paranoid ideation. British Journal of Clinical Psychology, 40, 261−265. Martin, J. A., & Penn, D. L. (2002). Attributional style in schizophrenia. Schizophrenia Bulletin, 28, 131−141. Mazza, M., De Risio, A., Surian, L., Roncone, R., & Casacchia, M. (2001). Selective impairments of theory of mind in people with schizophrenia. Schizophrenia Research, 47, 299−308. McCabe, R., Heath, C., Burns, T., & Priebe, S. (2002). Engagement of patients with psychosis in the consultation. British Medical Journal, 325, 1148−1151. McGhie, A., & Chapman, J. (1961). Disorders of attention and perception in early schizophrenia. British Journal of Medical Psychology, 34, 103−116. McGlashan, T. H., Levy, S. T., & Carpenter, W. T. (1975). Integration and sealing over: Clinically distinct recovery styles. Archives of General Psychiatry, 32, 1269−1272. McKay, R., Langdon, R., & Coltheart, M. (2005). Paranoia, persecutory delusions and attributional biases. Psychiatry Research, 136, 233−245. McReynolds, P. (1960). Anxiety, perception and schizophrenia. In D. D. Jackson (Ed.), The etiology of schizophrenia (pp. 248−292). New York: Basic Books. Mitchley, N. J., Barber, J., Gray, J. M., Brooks, D. N., & Livingstone, M. G. (1998). Comprehension of irony in schizophrenia. Cognitive Neuropsychiatry, 3, 127−138. Moritz, S., & Woodward, T. S. (2004). Plausibility judgement in schizophrenic patients. German Journal of Psychiatry, 7, 66−74. Moritz, S., & Woodward, T. S. (2005). Jumping to conclusions in delusional and non-delusional schizophrenic patients. British Journal of Clinical Psychology, 44, 193−207. Moritz, S., & Woodward, T. S. (2006a). Metacognitive control over false memories. Current Psychiatry Reports, 8, 184−190. Moritz, S., & Woodward, T. S. (2006b). A generalised bias against disconfirmatory evidence (BADE) in schizophrenia. Psychiatry Research, 142, 157−165. Mortimer, A. M., Bentham, P., McKay, A. P., Quemada, I., Clare, L., Eastwood, N., et al. (1996). Delusions in schizophrenia. Cognitive Neuropsychiatry, 1, 289−303. Murray, R. M., Grech, A., Phillips, P., & Johnson, S. (2003). What is the relationship between substance abuse and schizophrenia? In R. M. Murray (Ed.), The epidemiology of schizophrenia (pp. 317−342). Cambridge: Cambridge University Press. Myin-Germeys, I., Delespaul, P., & van Os, J. (2005). Behavioural sensitization to daily life stress in psychosis. Psychological Medicine, 35, 733−741. Myin-Germeys, I., & Krabbendam, L. (2003). Continuity of psychotic symptoms in the community. Current Opinion in Psychiatry, 16, 443−449. Naeem, F., Kingdon, D., & Turkington, D. (2006). Cognitive behaviour therapy for schizophrenia: Relationship between anxiety symptoms and therapy. Psychology and Psychotherapy, 79, 153−164. Norman, R. M., & Malla, A. K. (1994). Correlations over time between dysphoric mood and symptomatology in schizophrenia. Comprehensive Psychiatry, 35, 34−38. O'Leary, D. S., Flaum, M., Kesler, M. L., Flashman, L. A., Arndt, S., & Andreasen, N. C. (2000). Cognitive correlates of the negative, disorganized, and psychotic symptom dimensions of schizophrenia. Journal of Neuropsychiatry and Clinical Neurosciences, 12, 4−15. Olfson, M., Lewis-Fernández, R., Feder, A., Gameroff, M. J., Pilowsky, D., & Fuentes, M. (2002). Psychotic symptoms in an urban general medicine practice. American Journal of Psychiatry, 159, 1412−1419. Oltmanns, T. F. (1988). Approaches to the definition and study of delusions. In T. F. Oltmanns & B. A. Maher (Eds.), Delusional beliefs (pp. 3−12). New York: Wiley. Östling, S., & Skoog, I. (2002). Psychotic symptoms and paranoid ideation in a nondemented population-based sample of the very old. Archives of General Psychiatry, 59, 53−59. Peters, E., & Garety, P. (2006). Cognitive functioning in delusions. Behaviour Research and Therapy, 44, 481−514. Peters, E. R., Joseph, S. A., & Garety, P. A. (1999). The measurement of delusional ideation in the normal population: Introducing the PDI (Peters et al Delusions Inventory). Schizophrenia Bulletin, 25, 553−576. Peterson, C., Semmel, A., Von Baeyer, C., Abramson, L., Metalsky, G. I., & Seligman, M. E. P. (1982). The attributional style questionnaire. Cognitive Therapy and Research, 3, 287−300. Pickup, G. J., & Frith, C. D. (2001). Theory of mind impairments in schizophrenia. Psychological Medicine, 31, 207−220.

D. Freeman / Clinical Psychology Review 27 (2007) 425–457

457

Poulton, R., Caspi, A., Moffitt, T. E., Cannon, M., Murray, R., & Harrington, H. (2000). Children's self-reported psychotic symptoms and adult schizophreniform disorder. Archives of General Psychiatry, 57, 1053−1058. Premack, D., & Woodruff, G. (1978). Does the chimpanzee have a theory of mind? Behavioural and Brain Sciences, 4, 515−526. Randall, F., Corcoran, R., Day, J. C., & Bentall, R. P. (2003). Attention, theory of mind, and causal attributions in people with persecutory delusions. Cognitive Neuropsychiatry, 8, 287−294. Robins, L. N., Helzer, J. E., Croughan, J., & Ratcliff, K. A. (1981). National Institute of Mental Health Diagnostic Interview Schedule. Archives of General Psychiatry, 38, 381−389. Roncone, R., Falloon, I. R. H., Mazza, M., De Risio, A., Pollice, R., Necozione, S., et al. (2002). Is theory of mind in schizophrenia more strongly associated with clinical and social functioning than with neurocognitive deficits? Psychopathology, 35, 280−288. Rubin, E. H., Drevets, W. C., & Burke, W. J. (1988). The nature of psychotic symptoms in senile dementia of the Alzheimer type. Journal of Geriatric Psychiatry and Neurology, 1, 16−20. Russell, T. A., Reynaud, E., Herba, C., Morris, R., & Corcoran, R. (2006). Do you see what I see? Interpretations of intentional movement in schizophrenia. Schizophrenia Research, 81, 101−111. Salkovskis, P. M. (1991). The importance of behaviour in the maintenance of anxiety and panic: A cognitive account. Behavioural Psychotherapy, 19, 6−19. Sarfati, Y., Hardy-Baylé, M., Besche, C., & Widlöcher, D. (1997). Attribution of intentions to others in people with schizophrenia. Schizophrenia Research, 25, 199−209. Sartorius, N., Jablensky, A., Korten, A., Ernberg, G., Anker, M., Cooper, J. E., et al. (1986). Early manifestations and first-contact incidence of schizophrenia in different cultures. Psychological Medicine, 16, 909−928. Sax, K. W., Strakowski, S. M., Keck, P. E., Upadhyaya, V. H., West, S. A., & McElroy, S. L. (1996). Relationships among negative, positive and depressive symptoms in schizophrenia and psychotic depression. British Journal of Psychiatry, 168, 69−71. Schulze, T. G., Ohlraun, S., Czerski, P. M., et al. (2005). Genotype–phenotype studies in bipolar disorder showing association between the DAOA/ G30 locus and persecutory delusions. American Journal of Psychiatry, 162, 2101−2108. Sharp, H. M., Fear, C. F., & Healy, D. (1997). Attributional style and delusions: An investigation based on delusional content. European Psychiatry, 12, 1−7. Sheehan, D. V., Lecrubier, Y., Sheehan, K. H., Amorim, P., Janavs, J., Weiller, E., et al. (1998). The Mini-International Neuropsychiatric Interview. Journal of Clinical Psychiatry, 59(s20), 22−33. Snyder, K. (2006). Kurt Snyder's personal experience with schizophrenia. Schizophrenia Bulletin, 32, 209−211. Smith, B., Fowler, D., Freeman, D., Bebbington, P., Bashforth, H., Garety, P., Kuipers, E., & Dunn, G. (2006). Emotion and psychosis: Direct links between schematic beliefs, emotion and delusions and hallucinations. Schizophrenia Research, 86, 181−188. Smith, N., Freeman, D., & Kuipers, E. (2005). Grandiose delusions: An experimental investigation of the delusion-as-defence hypothesis. Journal of Nervous and Mental Disease, 193, 480−487. Startup, H. (2004). Persecutory beliefs and catastrophic worry. D. Clin Psy thesis. University of London. Startup, H., Freeman, D., & Garety, P. A. (in press). Persecutory delusions and catastrophic worry in psychosis: Developing the understanding of delusion distress and persistence. Behaviour Research and Therapy. Strauss, J. S. (1969). Hallucinations and delusions as points on continua function. Archives of General Psychiatry, 20, 581−586. Thewissen, V., Myin-Germeys, I., Bentall, R., de Graaf, R., Vollebergh, W., & van Os, J. (2005). Hearing impairment and psychosis revisited. Schizophrenia Research, 76, 99−103. Tien, A. Y., & Anthony, J. C. (1990). Epidemiological analysis of alcohol and drug use as risk factors for psychotic experiences. Journal of Nervous and Mental Disease, 178, 473−480. Trimble, M. R. (1992). The schizophrenia-like psychosis of epilepsy. Neuropsychiatry, Neuropsychology, and Behavioural Neurology, 5, 103−107. Trower, P., & Chadwick, P. (1995). Pathways to defense of the self: A theory of two types of paranoia. Clinical Psychology. Science and Practice, 2, 263−278. Van Dael, F., Versmissen, D., Janssen, I., Myin-Germeys, I., van Os, J., & Krabbendam, L. (2006). Data gathering: Biased in psychosis? Schizophrenia Bulletin, 32, 341−351. Van Os, J., Hanssen, M., Bijl, R. V., & Ravelli, A. (2000). Strauss (1969) revisited: A psychosis continuum in the general population. Schizophrenia Research, 45, 11−20. Van Os, J., & Verdoux, H. (2003). Diagnosis and classification of schizophrenia: Categories versus dimensions, distributions versus disease. In R. M. Murray, P. B. Jones, J. E.Susser, & M. van Os (Eds.), The epidemiology of schizophrenia (pp. 364−410). Cambridge: Cambridge University Press. Van Os, J., Verdoux, H., Maurice-Tison, S., Gay, B., Liraud, F., Salamon, R., et al. (1999). Self-reported psychosis-like symptoms and the continuum of psychosis. Social Psychiatry and Psychiatric Epidemiology, 34, 459−462. Vázquez-Barquero, J. L., lastra, I., Nuñez, M. J. C., Castanedo, S. H., & Dunn, G. (1996). Patterns of positive and negative symptoms in first episode schizophrenia. British Journal of Psychiatry, 168, 693−701. Verdoux, H., Gindre, C., Sorbara, F., Tournier, M., & Swendsen, J. D. (2003). Effects of cannabis and psychosis vulnerability in daily life. Psychological Medicine, 33, 23−32. Verdoux, H., Maurice-Tison, S., Gay, B., van Os, J., Salamon, R., & Bourgeois, M. L. (1998). A survey of delusional ideation in primary-care patients. Psychological Medicine, 28, 127−134. Walston, F., Blennerhassett, R. C., & Charlton, B. G. (2000). Theory of mind, persecutory delusions and the somatic marker mechanism. Cognitive Neuropsychiatry, 5, 161−174. Wells, A. (1994). A multi-dimensional measure of worry: Development and preliminary validation of the anxious thoughts inventory. Anxiety, Stress, and Coping, 6, 289−299. Zimbardo, P. G., Andersen, S. M., & Kabat, L. G. (1981). Induced hearing deficit generates experimental paranoia. Science, 212, 1529−1531.