Chp10 Final

More Than One Independent Variable Laying Out a Factorial Design A Research Example hoosing a !et"een#$ub%ects Design

What is a factor?

 A factor  is  is an independent variable.

More Than One Independent Variable

What is a factorial design?

 A factorial design contains more than one independent variable. The effect of psychotherapy (IV 1) and antidepressant drugs (IV 2) on depression (DV).  A two factor experiment is the simplest factorial design.

More Than One Independent Variable

What information can a factorial design provide?

 A factorial design can provide information about both treatment and interaction effects.

More Than One Independent Variable

What is a main effect? What determines the number of main effects in an experiment?

 A main effect is the action of a single IV on the DV. There can be as many main effects as independent variables.

More Than One Independent Variable

Provide an example of a main effect in a hypothetical study of exercise and depression.

 An eperimenter studies the effects of eercise intensity (IV1) and duration (IV 2) on depression (DV). If eercise intensity or duration separately reduced depression! these "ould constitute main effects.

More Than One Independent Variable

o! do !e determine !hether !e have main effects in our experiment?

#erform an appropriate statistical test.

More Than One Independent Variable

In a " x # x # study$ ho! many IVs and treatment conditions are there?

There are $ independent variables and 1% treatment conditions.

More Than One Independent Variable

Provide an example of a " x # x # study.

The independent variables "ere the perpetrator&s gender (male or female)! relationship to the child (parent! step'parent! or parent&s partner)! and severity of the abuse (neurological damage! broen bones! or bruising). The dependent variable "as sentence length.

More Than One Independent Variable

What is an interaction?

 An interaction is the oint effect of t"o or more IVs on the DV. *hen there is an interaction! the effect of one IV is different across levels of the other IV.

More Than One Independent Variable

Provide an example of an interaction.

If the antidepressant #ail produced greater reductions in depression in the +ognitive ,ehavior Therapy (+,T) condition than the *aiting -ist condition! this "ould illustrate an interaction bet"een drug and psychotherapy.

More Than One Independent Variable

What is a higher%order interaction?

 A higher-order interaction is an interaction among three or more IVs. Interpretation can be difficult "hen more than three IVs interact in an eperiment.

More Than One Independent Variable

Provide an example of a higher%order interaction.

 A previous hypothetical study eamined the effect of a perpetrator&s gender (male or female)! relationship to the child (parent! step'parent! or parent&s partner)! and severity of the abuse (neurological damage! broen bones! or bruising) on sentencing.

More Than One Independent Variable

Provide an example of a higher%order interaction.

There "ould be a higher-order interaction if the perpetrator&s gender! relationship to the child! and severity of abuse ointly determined sentence length.

More Than One Independent Variable

o! many interactions are possible in a study !ith three IVs?

 Assign letters (A! ,! +) to the independent variables. Identify all uniue t"o' and three' treatment combinations. /or three independent variables! these include  A,! A+! ,+! and A,+. A,+ is the higher'order  interaction.

More Than One Independent Variable

o! does an interaction affect the interpretation of our results?

 An interaction &uali'ies a main effect! "arning us that there may be limits or eceptions to the effect of an IV on the DV. *hen there is an interaction! "e must consider both IVs! because the effects of one factor "ill depend on the levels of the other factor.

More Than One Independent Variable

&xplain the factor%labeling method.

The factor-labeling method lists the t"o factors in parentheses after the numerical notation. /or eample! 2  2 (Type of 0ame  -ength of 0ame).

'aying Out a (actorial )esign

&xplain the factor and levels method.

This method lists the t"o factors and their respective levels after the numerical notation. /or eample! 2  2 (Type of 0ame given! nicname  -ength of 0ame short! long).

'aying Out a (actorial )esign

What advantage does the factor and levels method have over the factor%labeling method?

The factor and levels method provides more detailed information about the design than the factor'labeling method.

'aying Out a (actorial )esign

Why use a factorial design instead of t!o separate univariate experiments?

 A factorial design is more efficient since it combines several one'factor eperiments and allo"s us to study interactions.  A factorial design can achieve greater eternal validity since it can better recreate the compleity of the multivariate environment.

* +esearch &xample

Why should !e ,eep bet!een%sub-ects designs simple?

#ractical limitations include  number of subects  time  interpretability of results

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hoosing a /et!een%0ub-ects )esign