Interaction contrasts in repeated measures designs

Specific information concerning the nature of interaction effects in factorial designs may be obtained through the use of tetrad contrasts. Empirical familywise Type I error rates and power rates associated with 10 procedures for conducting tetrad contrasts in groups‐by‐trials repeated measures designs were obtained when the assumptions of multisample sphericity and multivariate normality were not satisfied. Only three procedures provided acceptable control of familywise Type I error rates under the assumption violation conditions. These procedures relied on a test statistic formed using an estimate of the standard error of the contrast which was based on only that data used in defining the contrast, in combination with either a Studentized maximum modulus, Hochberg (1988) step‐up Bonferroni, or Shaffer (1986) modified sequentially rejective Bonferroni critical value. Minimal power differences between these three procedures were observed.