Using a repeated measures ANOVA to analyze the data from a pretest-posttest design: A potentially confusing task.

The pretest-posttest control group design (or an extension of it) is a highly prestigious experimental design. A popular analytic strategy involves subjecting the data provided by this design to a repeated measures analysis of variance (ANOVA). Unfortunately, the statistical results yielded by this type of analysis can easily be misinterpreted, since the score model underlying the analysis is not correct. Examples from recently published articles are used to demonstrate that this statistical procedure has led to (a) incorrect statements regarding treatment effects, (b) completely redundant reanalyses of the same data, and (c) problems with respect to post hoc investigations. 2 alternative strategies-gain scores and covariance-are discussed and compared. (19 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)