Standard Article

Effect Modification

  1. Barbara McKnight

Published Online: 15 JUL 2005

DOI: 10.1002/0470011815.b2a03056

Encyclopedia of Biostatistics

Encyclopedia of Biostatistics

How to Cite

McKnight, B. 2005. Effect Modification. Encyclopedia of Biostatistics. 3.

Author Information

  1. University of Washington, Seattle, WA, USA

Publication History

  1. Published Online: 15 JUL 2005


Effect modification occurs when a measure of the association between an exposure and the risk of disease is modified, or changes, with values of a third variable called the effect modifier. For a given measure of association between exposure and disease risk, there is usually a corresponding regression model scale on which the presence of effect modification corresponds to the presence of statistical interaction between exposure and the effect modifying variable. This correspondence is described for several additive and multiplicative measures of association.


  • measures of association;
  • interaction;
  • multiplicative model;
  • additive model