Get access

Robust tests of equivalence for k independent groups


Correspondence should be addressed to Robert Cribbie, Quantitative Methods Program, Department of Psychology, York University, Toronto, ON, Canada M3J 1P3. (e-mail:


A common question of interest to researchers in psychology is the equivalence of two or more groups. Failure to reject the null hypothesis of traditional hypothesis tests such as the ANOVA F-test (i.e., H0: μ1 = … = μk) does not imply the equivalence of the population means. Researchers interested in determining the equivalence of k independent groups should apply a one-way test of equivalence (e.g., Wellek, 2003). The goals of this study were to investigate the robustness of the one-way Wellek test of equivalence to violations of homogeneity of variance assumption, and compare the Type I error rates and power of the Wellek test with a heteroscedastic version which was based on the logic of the one-way Welch (1951) F-test. The results indicate that the proposed Wellek–Welch test was insensitive to violations of the homogeneity of variance assumption, whereas the original Wellek test was not appropriate when the population variances were not equal.