Question

A cohort study was undertaken to examine the association between high lipid level and coronary heart disease. 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, and the age of each subject was recorded. The following data describes the study participants:

                              Developed CHD     No CHD
EXPOSED (High lipid level)
                  young                 20          3980
                    old                 200             5800

UNEXPOSED (Low or normal lipid level)
                  young               18                6982
                     old                    65          2935

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

Format: (x)/(y)=(z)

where,

X & Y are fractions

X is Step 1

Y is Step 2

Z is the crude measure of association

Hint: You will have to combine the two tables, young and old based on exposures so that you create the standard 2x2 table with exposed and nonexposed rows.

Interpret the crude measure you just calculated.

For the same cohort study, perform a stratified analysis and calculate the appropriate stratum-specific ratio measures of association (one for young, one for old). What are they?

Do the data provide evidence of effect measure modification? Justify your answer.

Answer 1