Contrast analysis for scale differences

Research on tests for scale equality, that are robust to violations of the distributional normality assumption, have focused exclusively on an overall test statistic and have not examined procedures for identifying specific differences in multiple group designs. The present study compares four contrast analysis procedures for scale differences in the single factor four group design. Two data transformations are considered under several conbinations of variance difference, sample sizes, and distributional forms.The results indicate that no single transformation or analysis procedure is uniformly superior in controlling the familywise error rate or in statistical power. The relationship between sample size and variances is a major factor in selecting a contrast analysis procedure.