Researchers are often interested in testing for the equivalence of population variances.Traditional difference-based procedures are appropriate to answer questions about differences in some statistic (e.g., variances, etc.). However, if a researcher is interested in evaluating the equivalence of population variances, it is more appropriate to use a procedure specifically designed to determine equivalence. A simulation study was used to compare newly developed equivalence-based tests to difference-based variance homogeneity tests under common data conditions. Results demonstrated that traditional difference-based tests assess equality of variances from the wrong perspective, and that the proposed Levene-Wellek-Welch test for equivalence of group variances using the absolute deviations from the median was the best performing test for detectingequivalence. An R function is provided in order to facilitate use of this test for equivalence of population variances.
keywords: equivalence testing, homogeneity of variances, ANOVA, dispersion 3
Equivalence of Population Variances:
Synchronizing the Objective and AnalysisHomogeneity of variances occurs when population distributions have similar dispersion. Researchers are becoming increasingly interested in the properties of their data aside from central tendency, such as dispersion. For instance, Borkenau, Hrebícková, Kuppens, Realo, and Allik (2013) hypothesized that self-reported personality scores would have similar variability across males and females. Salgado (1995) examined whether the variability in validity coefficients in self-report tests for a specific construct was equivalent to the variability in validity coefficients in psychomotor tests evaluated by an external rater of the same construct. A more well-known reason for exploring variances is to verify the homogeneity of variances assumption related to traditional parametric tests of mean differences. Regardless of the reason, researchers need a valid test for assessing questions related to variability.There has been substantial research on different tests that can be used to test for differences in variances. This paper discusses whether traditional tests of variance homogeneity address the problem of variance equality from the wrong perspective. We argue that to test for variance homogeneity, one should use equivalence tests because the research hypothesis of variance equality is properly aligned with the alternate hypothesis, not the null hypothesis. To that end, we first situate a test for equality of group variances within the equivalence testing framework. Even though difference-based procedures are appropriate to answer questions about differences in some statistic (e.g., means, variances, etc.), these procedures are not appropriate to address questions related to equivalence. Then, the main goal of this paper is to compare our newly developed tests 4 for equivalence of group variances to currently recommended variance homogeneity tests under data conditions common in educational and psychologic...