A cohort study was undertaken to examine the association betweenhigh lipid level and coronary heart disease (CHD). Participantswere classified as having either a high lipid level (exposed) or alow or normal lipid level (unexposed). Because age is associatedwith both lipid level and risk of heart disease, age was considereda potential confounder or effect modifier and the age of eachsubject was recorded. The following data describes the studyparticipants: Overall, there were 11,000 young participants and9,000 old participants. Of the 4,000 young participants with highlipid levels, 20 of them developed CHD. Of the 6,000 oldparticipants with high lipid levels, 200 of them developed CHD. Inthe unexposed, 18 young and 65 old participants developed CHD..Calculate the appropriate crude ratio measure of associationcombining the data for young and old individuals. 3. Now, perform astratified analysis and calculate the appropriate stratum-specificratio measures of association. What are they? 4. Do the dataprovide evidence of effect measure modification on the ratio scale?Justify your answer.
