NOW YOU SEE IT, NOW YOU DONT - A COMPARISON OF TRADITIONAL VERSUS RANDOM-EFFECTS REGRESSION-MODELS IN THE ANALYSIS OF LONGITUDINAL FOLLOW-UP DATA FROM A CLINICAL-TRIAL

To illustrate the limitations of commonly used methods of handling mis sing data when using traditional analysis of variance (ANOVA) models a nd highlight the relative advantages of random-effects regression mode ls, multiple analytic strategies were applied to follow-up data from a clinical trial. Traditional ANOVA and random-effects models produced similar results when underlying assumptions were met and data were com plete. However, analyses based on subsamples, to which investigators w ould have been limited with traditional models, would have led to diff erent:conclusions about treatment effects over time than analyses base d on intention-to-treat samples using tandem-effects regression models . These findings underscore the advantages of models that use all data collected and the importance of complete data collection to minimize sample bias.