At a nominal alpha level of .01 and homogeneous variances, all of the proce
dures, with the exception of the NK procedure, maintained the familywise alpha
within the limits of Bradley's liberal criterion (actual aFW < 1.5ocnominal). Because
of its focus on Type I error control at the level of the individual contrast, the New
man-Keuls procedure became overly liberal in familywise Type I error control
with more than three groups in the ANOVA. The DN procedure and the modified
Bonferroni procedures maintained familywise alpha within Bradley's conserva
tive criterion (actual ocFW < l.locnominal), with the exception of the HS procedure
with five groups (aFW = .012). However, none of the procedures was able to
maintain familywise alpha within even Bradley's liberal criterion under unequal
variances. The empirical Type I error rate estimates became nearly five times the
nominal alpha level for all procedures with five groups and the most extreme
variance heterogeneity examined (1:1:1:1:13).