1. A cohort study examined the association between lipid level and coronary heart disease (CHD). All subjects were initially free of CHD. Participants were classified as having either a high lipid level (exposed) or normal lipid level (unexposed) at baseline and the presence or absence of CHD after 10 years of follow-up. Because age is associated with both lipid level and CHD, age was considered a potential confounder and the age of each subject at baseline was recorded. The following data describes the study participants: Baseline Lipid Levels Baseline Age High Normal No No CHD CHD CHD CHD Young Old 20 3980 18 6982 200 5800 65 2935 (a) Calculate the crude risk ratio of coronary heart disease comparing study participants with high lipid levels to those with normal lipid levels. Provide a brief interpretation of this association. [4 points] (b) Calculate the risk ratio of coronary heart disease comparing study participants with high lipid levels to those with normal lipid levels separately for each age stratum. Provide a brief interpretation of these associations. [4 points] (c) Do these data provide any evidence of multiplicative interaction? Pro- vide a brief justification for your answer. [4 points] 2. A case-control study examined the association between pulmonary hyper- tension among women who take diet drugs to lose weight. The crude odds ratio of pulmonary hypertension comparing diet drug users to non-users is 17.0 and the age adjusted odds ratio is 5.0. (a) Is there any evidence that age is a confounder in this study? Provide a brief justification for your answer. [4 points] (b) Could the omission of men from this study result in bias due to con- founding by sex? Provide a brief justification for your answer. [4 points]