A Randomization Permutation Test for Single Subject Mediation

David P. MacKinnon, Heather L. Smyth, Jennifer Somers, Emily Ho, Julia Norget, Milica Miočević

Research output: Contribution to journalArticlepeer-review

4 Scopus citations


In response to the importance of individual-level effects, the purpose of this paper is to describe the new randomization permutation (RP) test for a mediation mechanism for a single subject. We extend seminal work on permutation tests for individual-level data by proposing a test for mediation for one person. The method requires random assignment to the levels of the treatment variable at each measurement occasion, and repeated measures of the mediator and outcome from one subject. If several assumptions are met, the process by which a treatment changes an outcome can be statistically evaluated for a single subject, using the permutation mediation test method and the permutation confidence interval method for residuals. A simulation study evaluated the statistical properties of the new method suggesting that at least eight repeated measures are needed to control Type I error rates and larger sample sizes are needed for power approaching.8 even for large effects. The RP mediation test is a promising method for elucidating intraindividual processes of change that may inform personalized medicine and tailoring of process-based treatments for one subject.

Original languageEnglish (US)
Pages (from-to)54-65
Number of pages12
JournalEvaluation and the Health Professions
Issue number1
StatePublished - Mar 2022


  • active ingredients
  • idiographic methods
  • mediating mechanisms
  • permutation tests
  • single subject

ASJC Scopus subject areas

  • Health Policy


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