Reference Work Entry

Encyclopedia of Public Health

pp 320-321

Effect Modifiers


Moderators of effect size


An effect modifier is a factor, such as age or disease severity, which alters the effectiveness of an intervention. It is important that these effect modifiers be identified as they may explain apparent differences in the findings of the primary studies included in the meta-analysis. Effect modification means that the relation of the exposure and outcome is different depending on which stratum of the effect modifier we are in. Another series of possible “effect modifiers” in meta-analysis relate to study design. If the moderator proves to be significant, the meta-analyst should present an average effect size and confidence interval for each grouping of studies.

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