Using Nonnaive Participants Can Reduce Effect Sizes

Jesse Chandler, Gabriele Paolacci, Eyal Peer, Pam Mueller, Kate A. Ratliff

Research output: Contribution to journalArticlepeer-review

124 Scopus citations


Although researchers often assume their participants are naive to experimental materials, this is not always the case. We investigated how prior exposure to a task affects subsequent experimental results. Participants in this study completed the same set of 12 experimental tasks at two points in time, first as a part of the Many Labs replication project and again a few days, a week, or a month later. Effect sizes were markedly lower in the second wave than in the first. The reduction was most pronounced when participants were assigned to a different condition in the second wave. We discuss the methodological implications of these findings.

Original languageEnglish
Pages (from-to)1131-1139
Number of pages9
JournalPsychological Science
Issue number7
StatePublished - 16 Jul 2015

Bibliographical note

Publisher Copyright:
© 2015, The Author(s) 2015.


  • effect sizes
  • judgment and decision making
  • nonnaïveté
  • open data
  • open materials
  • panel conditioning
  • repeated participation
  • research methods


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