EPI 202 Lab 5.docx - EPI 202 Lab 5 The table below show data from a hypothetical cohort study of the relationship between aspirin use(yes versus no and

# EPI 202 Lab 5.docx - EPI 202 Lab 5 The table below show...

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EPI 202 Lab 5 The table below show data from a hypothetical cohort study of the relationship between aspirin use (yes versus no) and 5-year risk of stroke (assume there was no loss to follow-up or competing risks). The tables are stratified by sex, a suspected confounder. Male ASA No ASA Total Female ASA No ASA Total Stroke 60 40 100 Smoke 75 60 135 No stroke 90 10 100 No Smoke 75 40 115 Total 150 50 200 Total 150 100 250 1. Using standardization, compute the cumulative incidence ration for the total study population. Briefly interpret your results. A: Standardization Pr [ Y a = 1 = 1 ] Pr [ Y a = 0 = 1 ] = Pr [ Y = 1 | A = 1, L = 0 ] Pr [ L = 0 ] + Pr [ Y = 1 | A = 1, L = 1 ] Pr [ L = 1 ] Pr [ Y = 1 | A = 0, L = 0 ] Pr [ L = 0 ] + Pr [ Y = 1 | A = 0, L = 1 ] Pr [ L = 1 ] ¿ 75 150 × 250 450 + 60 150 × 200 450 60 100 × 250 450 + 40 50 × 200 450 = 125 + 80 150 + 160 = 205 310 = 0.66129 5 years If everyone in the study had taken aspirin, we would have observed 0.66 times the 5-year cumulative incidence of stroke compared to if no one in the study had taken aspirin, assuming no residual confounding by sex, no confounding by other variables, no selection bias and no information bias. B: Traditional Approach ^ CIR = ^ R 1 ^ R 0 = a i T i N 1 i b i T i N oi = 60 150 × 200 + 75 150 × 250 40 50 × 200 + 60 100 × 250 = 0.66129 5 years If everyone in the study had taken aspirin, we would have observed 0.66 times the 5-year cumulative incidence of stroke compared to if no one in the study had taken aspirin, assuming no residual confounding by sex, no confounding by other variables, no selection bias and no information bias.

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