QUESTION 1 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. o o o o QUESTION 2 1. 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 A study used self-administered mail questionnaires to gather data on height and weight in order to calculate a measure of obesity. Which of the following types of problems were likely avoided by this method of data collection, and why? o o o o o Interviewer bias Exposure misclassification Confounding Selection bias Loss-to-follow-up QUESTION 3 1. The association between cellular telephone use and the risk of brain cancer was investigated in a casecontrol study. The study included 475 cases and 400 controls and the following results were seen: Cellular Yes Phone No User Total Cases 270 Controls 200 205 200 475 400 o o 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. Males Cellular Yes Phone No User Cases 242 Controls 150 Females Cases Yes 28 100 50 No o 105 Controls 50 150 Calculate the stratum-specific odds ratios. o o Is gender a confounder in this study? Briefly justify your answer. Is gender an effect measure modifier in this study? Briefly justify your answer
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