Epidemiology Summary – Weeks 1 to 6

Epidemiology summary – weeks 1 to 6 Defnition: Study Defnition: Study of distribution & determinants of health-related events in specic populations, & applying it to prevent & control health problems Risk actor: actor: Factors that are positively associated with risk of disease development but are not sucient to cause the disease e!g! smoking is a risk factor for "#$% Prevalence: Freuency Prevalence: Freuency of e'isting cases in a predened population at a given point of time (eriod prevalence ) over a longer time% Incidence: Incidence: *umber of new cases of disease during a specied time period period  number of people e'posed !umulative incidence: *umber incidence:  *umber of people who get a disease during a specied period period number of people free of disease in the population at risk at beginning of the period! Population attri"uta"le risk : + of disease in whole population that can be attributed to a particular e'posure e'posure Risk di#erence: di#erence: $ierence in rates of occurrence between e'posed & une'posed groups in population !onounding: hen !onounding: hen another e'posure e'ists in the study population! .inks both disease & e'posure being studied $ortality: $eath $ortality: $eath rates! $or"idity: $or"idity: /llness rather than mortality %ealt& determinants: determinants: 0nderlying factors e!g! env, social, econ% that are responsible responsible for health & disease D'(): 1ears D'():  1ears of lost life 2 years lost to disability *+,DIE* See *+,DIE* See the triangle% 3cological: 3cological: 4bservation 4% made on groups not individuals%! 3!g! .iver disease and alcohol consumption 5-sectional: 6ssess e'posure & outcome simultaneously! *o evaluation of temporality! 3!g! cannabis and depression "ase-control: "ase-control: 7ackwards in time to look for e'posure! Start with diseased state! 8are diseases, odds ratio (rospective "ohort: Forwards in time! Start with healthy people 2 e'posure and without e'posure and see who gets the disease! 8etrospective "ohort: Forwards in time! 3'posure is dened at time in past! *o knowledge of possible outcomes!

*u-cient .ecessary 6 cause is 6 cause is sucient when it necessary if an inevitably outcome cannot produces or develop in its initiates an absence! outcome Smoking is not  1ou  1ou must have sucient to cause the lung cancer mycobacterium Some smoke tuberculosis tuberculosis in ;t get it% tuberculosis $emorise t&is ta"le/ $isease lung cancer%  )es  )es .o +otal 8isk factor  )es  )es 6 7 627 4r .o " $ "2$ e'posur +ot 62" 72$ e al 0dds ratio: 6ssociation ratio: 6ssociation of e'posure to disease 0sed in case control & cross sectional studies ? for when disease is rare% Formula: (Proves hypothesis)/(disproves hypothesis)/(disproves it)

( ( )( )

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Exposure Exposure with disease  Exp ¿= ÷  Noexposur  No exposuree with disease  No e  A B = AD ÷ C   D BC 

Relative risk : For cohort & 8"9s 8e ) 6@627%, 8u ) "@"2$% 88 ) 8e@8u ) 6 5 "2$%%@" 5 627%% Risk di#erenceattri"uta"le risk  )  ) 8e-8u 'ttri"uta"le raction: raction: + of cases attributed to e'posure: 8e8u%@8e%'A==+ /f 88@48 includes A: *o di, includes)di  Population attri"uta"le risk : B6@ 62"%C5A==+ *tandard Error: Error: $istance from sample statistic to population parameter! 6s n increases, S3 decreases! 6s S$ increases, S3 increases as well!

SE =

SD

√ n

!onfdence interval: interval : /nterval around sample statistic that captures population parameter )  x     ± T

mult multipl iplie ierr × SE( x  ¯x )

1ou should get a range of values% !I "etween  means:

multip ipli lier er × SE( x¯ 1− x ( x¯ 1− x¯ 2 ) ± T mult ¯ 2) /f "/ includes Dero: *o di, if includes ) di!

4f course, 8"9 and eta-6nalyses +2test ? +2test ? E kinds: A sample mean vs! hypo%,  sample  sep! means% paired

Esta"lis&ing causation: A! 9empora emporall relat relation ionshi ship p GG% GG% "ause must precede event ! (lau lausibi sibillity ity "linical tests E! "on "onsist istency ncy Several studies showing similar results H! Stre Streng ngth th of of asso associ ciat atio ion n $egree of association between cause and eect