A comparison of methods for increasing power in randomized between-subjects designs.

Power in a randomized between-subjects design can be enhanced by increasing sample size or increasing alpha level. This article compares 2 other methods of increasing power by reducing within-group error. (a) by adding a pretest to the design and using analysis of covariance (ANCOVA) and (b) by increasing the length of the posttest and using analysis of variance (ANOVA)