Increasing Statistical Power in Mediation Models Without Increasing Sample Size

Matthew S. Fritz, Matthew G. Cox, David Mackinnon

Research output: Contribution to journalArticlepeer-review

35 Scopus citations


Inadequate statistical power to detect treatment effects in health research is a problem that is compounded when testing for mediation. In general, the preferred strategy for increasing power is to increase the sample size, but there are many situations where additional participants cannot be recruited, necessitating the use of other methods to increase statistical power. Many of these other strategies, commonly applied to analysis of variance and multiple regression models, can be applied to mediation models with similar results. Additional predictors or blocking variables will increase or decrease statistical power, however, depending on whether these variables are related to the mediator, the outcome, or both. The effect of these two methods on the power for tests of mediation is illustrated through the use of simulations. Implications for health researchers using these methods are discussed.

Original languageEnglish (US)
Pages (from-to)343-366
Number of pages24
JournalEvaluation and the Health Professions
Issue number3
StatePublished - Sep 18 2015


  • mediation
  • sample size
  • statistical power

ASJC Scopus subject areas

  • Health Policy


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