摘要：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.
关键词：Welch’s t-test; Student’s t-test; homogeneity of variance; Levene’s test; Homoscedasticity;
statistical power; type 1 error; type 2 error
