Additional file to "Why Psychologists Should by Default Use Welch's t-test Instead of Student's t-test." (in press for the International Review of Social Psychology)

Marie Delacre, Daniel Lakens and Christophe Leys
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Daniel Lakens: Eindhoven University of Technology

No dqck7, OSF Preprints from Center for Open Science

Abstract: When comparing two independent groups, researchers in Psychology commonly use Student’s t-test. Assumptions of normality and of homogeneity of variance underlie this test. More often than not, when these conditions are not met, Student’s t-test can be severely biased, and leads to invalid statistical inferences. Moreover, we argue that the assumption of equal variances will seldom hold in psychological research and that choosing between Student’s t-test or Welch’s t-test based on the outcomes of a test of the equality of variances often fails to provide an appropriate answer. We show that the Welch’s t-test provides a better control of Type 1 error rates when the assumption of homogeneity of variance is not met, and loses little robustness compared to Student’s t-test when the assumptions are met. We argue that Welch’s t-test should be used as a default strategy.

Date: 2017-02-17
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Persistent link: https://EconPapers.repec.org/RePEc:osf:osfxxx:dqck7

DOI: 10.31219/osf.io/dqck7

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