Collection: Methodological resources for social psychologists

Research article

Why Psychologists Should by Default Use Welch’s t-test Instead of Student’s t-test



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.


Publisher’s Note: A correction article relating to this paper has been published and can be found at


Welch’s t-testStudent’s t-testhomogeneity of varianceLevene’s testHomoscedasticitystatistical powertype 1 errortype 2 error
  • Year: 2017
  • Volume: 30 Issue: 1
  • Page/Article: 92-101
  • DOI: 10.5334/irsp.82
  • Published on 5 Apr 2017
  • Peer Reviewed