Question

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.

Answer 1

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