EPI202_2018_Stratified Count Data.pdf - Harvard TH Chan School of Public Health EPI202 \u2013 Epidemiologic Methods II Fall 2018 Harvard TH Chan School of

EPI202_2018_Stratified Count Data.pdf - Harvard TH Chan...

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Harvard TH Chan School of Public Health EPI202 – Epidemiologic Methods II Fall 2018 1 EPI202 – Epidemiologic Methods II Murray A. Mittleman, MD, DrPH Department of Epidemiology, Harvard TH Chan School of Public Health Module Stratified Data Analysis for Count Data (Closed Cohort and Cross sectional Studies) Harvard TH Chan School of Public Health EPI202 – Epidemiologic Methods II Fall 2018 2 Key Concepts Notation Hypothesis tests Point and interval estimates for the cumulative incidence ratio Point and interval estimates for the cumulative incidence difference
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Harvard TH Chan School of Public Health EPI202 – Epidemiologic Methods II Fall 2018 3 Notation for Count Data (closed cohort and cross sectional studies) Recall our notation for an unstratified table of count data in closed cohort or cross sectional studies: Notation E Ē Cases a b M 1 Non cases c d M 0 N 1 N 0 T Harvard TH Chan School of Public Health EPI202 – Epidemiologic Methods II Fall 2018 4 Notation for Count Data (closed cohort and cross sectional studies) Now we stratify the data by one or more confounding variables, so that each stratum consists of subjects who have, on average, the same risk for disease, with the possible exception of the exposure effect. We have i=1,...,I of these strata, which are formed by each unique combination of levelsof the confounding variables for which there are data. Notation E Ē Cases a i b i M 1i Non cases c i d i M 0i N 1i N 0i T i
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Harvard TH Chan School of Public Health EPI202 – Epidemiologic Methods II Fall 2018 5 Evans County Study Revisited 609 white men free of disease at baseline, are followed to investigate the association between the 7 year cumulative incidence of coronary heart disease (CHD) and endogenous catecholamines (CAT). We stratify by two potential confounders age group (<55 / 55+) electrocardiogram status (N=normal / A=abnormal). Age<55 ECG=N Age<55 ECG=A Age 55+ ECG=N Age 55+ ECG=A Cat Level Hi Low Hi Low Hi Low Hi Low Cases 1 17 3 7 9 15 14 5 Non cases 7 257 14 52 30 107 44 27 Total 8 274 17 59 39 122 58 32 CI 12.5 6.2 17.6 11.9 23.1 12.3 24.1 15.6 Harvard TH Chan School of Public Health EPI202 – Epidemiologic Methods II Fall 2018 6 Hypothesis Test for Unstratified Data Recall the hypothesis test statistic: In closed cohorts (count data) with no confounding, X = number of exposed cases = a E(X|H ) = number of exposed cases expected under H = total number of cases * Pr(E) = M (N /T) ) H | Var(X ] ) H | E(X - [X = Z 0 2 0 2 T N N M M = ) H | Var(X 3 0 1 0 1 0
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Harvard TH Chan School of Public Health EPI202 – Epidemiologic Methods II Fall 2018 7 Hypothesis Test for Stratified Data (1) In closed cohorts or cross sectional studies (count data) with confounding, we stratify the data on all confounding variables to form I strata We then calculate the test statistic: 2 1 H | X Var H | X E X 2 χ ~ Z 0 i I 1 i i 2 I 1 i 0 i I 1 i i i Harvard TH Chan School of Public Health EPI202 – Epidemiologic Methods II Fall 2018 8
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