Can tests for treatment group equality be improved?: The bootstrap and trimmed means conjecture


Department of Psychology, University of Southern California, Seeley G. Mudd Building, Room 501, Los Angeles, CA 90089-1061, USA


Westfall & Young's (1993) results suggest that by combining bootstrap methods with methods based on trimmed means researchers can obtain better Type I error control when testing for treatment group equality. Thus, the methods due to Alexander & Govern (1994), Box (1954), and Welch (1951) were compared under conditions of non-normality and variance heterogeneity when group sizes were unequal, conditions known to produce liberal rates of error. We found that, typically, in one-way designs better Type I error control can indeed be obtained when the bootstrap method is used in conjunction with test statistics based on trimmed means.