Why psychologists should by default use Welch's t-test instead of student's t-test

M. Delacre, D. Lakens, C. Leys

Research output: Contribution to journalArticleAcademicpeer-review

295 Citations (Scopus)
1634 Downloads (Pure)


When comparing two independent groups, psychology researchers commonly use Student's t-Tests. Assumptions of normality and 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 lead to invalid statistical inferences. Moreover, we argue that the assumption of equal variances will seldom hold in psychological research, and choosing between Student's t-Test and 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 it 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.

Original languageEnglish
Pages (from-to)92-101
Number of pages10
JournalInternational Review of Social Psychology
Issue number1
Publication statusPublished - 5 Apr 2017


  • Homogeneity of variance
  • Homoscedasticity
  • Levene's test
  • Statistical power
  • Student's t-Test
  • Type 1 error
  • Type 2 error
  • Welch's t-Test
  • type 2 error
  • Student's t-test
  • statistical power
  • Welch's t-test
  • type 1 error
  • homogeneity of variance


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