Standard least squares analysis of variance methods suffer from poor power under arbitrarily small departures from normality and fail to control the probability of a Type I error when standard assumptions are violated. This article describes a framework for robust estimation and testing that uses trimmed means with an approximate degrees of…

Three approaches to the analysis of main and interaction effect hypotheses in nonorthogonal designs were compared in a 2 x 2 design for data that was neither normal in form nor equal in variance. The Welch-James test with trimmed means and Winsorized variances provided excellent Type I error control. (SLD)

Results of a study of repeated measures stepwise multiple comparison procedures indicate that multiple range procedures modified according to Duncan's (1975) method and employing nonpooled omnibus or pairwise stepwise procedures are robust to violations of the multisample sphericity assumption and are typically more powerful than the usual range…

Kelley compared three methods for setting a confidence interval (CI) around Cohen's standardized mean difference statistic: the noncentral-"t"-based, percentile (PERC) bootstrap, and biased-corrected and accelerated (BCA) bootstrap methods under three conditions of nonnormality, eight cases of sample size, and six cases of population…

Reviews methods for analyzing repeated measures data in addition to the conventional and corrected degrees of freedom univariate and multivariate solutions. Reviews the literature regarding recent procedures with respect to robustness, ability to handle missing data, and availability of software to obtain numerical results. (SLD)

The Welch-James (WJ) and the Huynh Improved General Approximation (IGA) tests for interaction were examined with respect to Type I error in a between- by within-subjects repeated measures design when data were non-normal, non-spherical and heterogeneous, particularly when group sizes were unequal. The tests were computed with aligned ranks and…

The authors argue that a robust version of Cohen's effect size constructed by replacing population means with 20% trimmed means and the population standard deviation with the square root of a 20% Winsorized variance is a better measure of population separation than is Cohen's effect size. The authors investigated coverage probability for…

Examines the recommendations of H. Keselman, K. Carriere, and L. Lix (1993) regarding choice of sample size for obtaining robust tests of the repeated measures main and interaction hypotheses in a one Between-Subjects by one Within- Subjects design with a Welch-James type multivariate test when covariance matrices are heterogeneous. (SLD)

Nonparametric and robust statistics (those using trimmed means and Winsorized variances) were compared for their ability to detect treatment effects in the two-sample case. The use of two specialized tests, designed to be sensitive to treatment effects when data distributions are skewed to the right, is not supported by the analyses. (SLD)

This paper explains how to obtain generally robust and powerful analyses with any of the recommended nonorthogonal solutions by adapting a modification of the Welch-James procedure for comparing means when population variances are heterogeneous. Results from a Monte Carlo study support use of the procedure. (SLD)

Six stepwise multiple-comparison procedures for repeated-measures means were compared for their overall familywise rates of Type I error when multisample sphericity and multivariate normality were not satisfied. Robust stepwise procedures were identified by Keselman, Keselman, and Shaffer (1991) with respect to three definitions of power. (SLD)

The use of analysis of variance (ANOVA), multivariate analysis of variance (MANOVA), and analysis of covariance (ANCOVA) by educational researchers was studied through review of several prominent research journals. The analyses suggest that researchers rarely verify that validity assumptions are satisfied, and typically use analyses that are…

The approximate degrees of freedom Welch-James (WJ) and Brown-Forsythe (BF) procedures for testing within-subjects effects in multivariate groups by trials repeated measures designs were investigated under departures from covariance homogeneity and normality. Empirical Type I error and power rates were obtained for least-squares estimators and…