A monte carlo simulation study of the reliability of intraindividual variability

Ryne Estabrook, Kevin J. Grimm, Ryan P. Bowles

Research output: Contribution to journalArticlepeer-review

51 Scopus citations


Recent research has seen intraindividual variability become a useful technique to incorporate trial-to-trial variability into many types of psychological studies. Intraindividual variability, as measured by individual standard deviations (ISDs), has shown unique prediction to several types of positive and negative outcomes (Ram, Rabbit, Stollery, & Nesselroade, 2005). One unanswered question regarding measuring intraindividual variability is its reliability and the conditions under which optimal reliability is achieved. Monte Carlo simulation studies were conducted to determine the reliability of the ISD as compared with the intraindividual mean. The results indicate that ISDs generally have poor reliability and are sensitive to insufficient measurement occasions, poor test reliability, and unfavorable amounts and distributions of variability in the population. Secondary analysis of psychological data shows that use of individual standard deviations in unfavorable conditions leads to a marked reduction in statistical power, although careful adherence to underlying statistical assumptions allows their use as a basic research tool.

Original languageEnglish (US)
Pages (from-to)560-576
Number of pages17
JournalPsychology and aging
Issue number3
StatePublished - 2012
Externally publishedYes


  • ISD
  • Individual differences
  • Intraindividual variability
  • Reliability

ASJC Scopus subject areas

  • Social Psychology
  • Aging
  • Geriatrics and Gerontology


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