Abstract

Does psi exist? D. J. Bem (2011) conducted 9 studies with over 1,000 participants in an attempt to demonstrate that future events retroactively affect people's responses. Here we discuss several limitations of Bem's experiments on psi; in particular, we show that the data analysis was partly exploratory and that one-sided p values may overstate the statistical evidence against the null hypothesis. We reanalyze Bem's data with a default Bayesian t test and show that the evidence for psi is weak to nonexistent. We argue that in order to convince a skeptical audience of a controversial claim, one needs to conduct strictly confirmatory studies and analyze the results with statistical tests that are conservative rather than liberal. We conclude that Bem's p values do not indicate evidence in favor of precognition; instead, they indicate that experimental psychologists need to change the way they conduct their experiments and analyze their data.

Keywords

PsychologySkepticismNull hypothesisStatistical hypothesis testingTest (biology)Affect (linguistics)Bayesian probabilitySocial psychologyCognitive psychologyEconometricsEpistemologyStatisticsMathematicsPhilosophy

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Publication Info

Year
2011
Type
article
Volume
100
Issue
3
Pages
426-432
Citations
990
Access
Closed

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Eric‐Jan Wagenmakers, Ruud Wetzels, Denny Borsboom et al. (2011). Why psychologists must change the way they analyze their data: The case of psi: Comment on Bem (2011).. Journal of Personality and Social Psychology , 100 (3) , 426-432. https://doi.org/10.1037/a0022790

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DOI
10.1037/a0022790