Question 1. A cohort study was undertaken to examine the association between high lipid level and coronary heart disease (CHD). Participants were classified as having either a high lipid level (exposed) or a low or normal lipid level (unexposed). Because age is associated with both lipid level and risk of heart disease, age was considered a potential confounder or effect modifier and the age of each subject was recorded. The following data describes the study participants: Overall, there were 11,000 young participants and 9,000 old participants. Of the 4,000 young participants with high lipid levels, 20 of them developed CHD. Of the 6,000 old participants with high lipid levels, 200 of them developed CHD. In the unexposed, 18 young and 65 old participants developed CHD.

· Construct the appropriate two by two tables using the data given above. Be sure to label the cells and margins.

· Calculate the appropriate crude ratio measure of association combining the data for young and old individuals.

· Now, perform a stratified analysis and calculate the appropriate stratum-specific ratio measures of association. What are they?

· Do the data provide evidence of effect measure modification on the ratio scale? Justify your answer.

Question 2. Consider each of the following scenarios and state whether or not the variable in question is a confounder, and why.

· A study of the risk of pulmonary hypertension among women who take diet drugs to lose weight. The crude relative risk of pulmonary hypertension comparing diet drug users to non-users is 17.0 and the age adjusted relative risk is 5.0. Is age a confounder in this study?

· A cohort study of liver cancer among alcoholics. Incidence rates of liver cancer among alcoholic men are compared to a group of non-alcoholic men. Is gender a confounder in this study?

· A case-control study of the risk of beer consumption and oral cancer among men. In this study, cigarette smoking is associated with beer consumption and is a risk factor for oral cancer among both beer drinkers and nondrinkers. Is cigarette smoking a confounder in this study?

Question 3. The association between cellular telephone use and the risk of brain cancer was investigated in a case-control study. The study included 475 cases and 400 controls and the following results were seen:

Calculate the odds ratio based on these data.

· The p value for this odds ratio is 0.06. State your interpretation of this p-value.

Gender was considered a potential confounder and effect measure modifier in this study. The data were stratified into males and females in order to assess these issues.

Calculate the stratum-specific odds ratios.

· Is gender a confounder in this study? Briefly justify your answer.

· Is gender an effect measure modifier in this study? Briefly justify your answer.