Question

What is effect measure modification? What process does an epidemiologist use to assess the presence or absence of effect measure modification?

Answer 1

Effect Measure Modification:

If the magnitude of the risk ratio, rate ratio, odds ratio or risk difference) varies in different subgroups (strata) of the study population, there is effect modification. This differs from confounding, where we generally believe that the measure of effect (i.e. the RR, OR etc.) will be the same in each of the strata defined by levels of the confounding variable.

Stratification of the data by a possible effect measure modifying variable is a good method to test its presence or absence.

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