Of rowing boats, ocean liners and tests of the ANOVA homogeneity of variance assumption

Abstract One of the assumptions of analysis of variance (anova) is that the variances of the groups being compared are approximately equal. This assumption is routinely checked before doing an analysis, although some workers consider anova robust and do not bother and others avoid parametric procedures entirely. Two of the more commonly used heterogeneity tests are Bartlett's and Cochran's, although, as for most of these tests, they may well be more sensitive to violations of the anova assumptions than is anova itself. Simulations were used to examine how well these two tests protected anova against the problems created by variance heterogeneity. Although Cochran's test performed a little better than Bartlett's, both tests performed poorly, frequently disallowing perfectly valid analyses. Recommendations are made about how to proceed, given these results.