What is the role of two-wave designs in clinical research? Comment on Hageman and Arrindell.

Traditional beliefs about regression to the mean, difference scores (d-scores) and corrections for regression in determining the significance of individual person change have been challenged by proponents of growth curve modeling for the study of change. These challenges have generally not been adequately addressed by those proposing modifications to Jacobson's Reliable Change Index (RC). It is proposed that (1) two-wave designs and RC or variations of it are not very good methods for the scientific study of change, (2) multi-wave designs are better, (3) d-scores are unbiased data for analyzing two-wave studies, (4) RC is relatively more justifiable than most corrected or adjusted forms of RC, (5) the more appropriate place for two-wave designs and RC are in program or outcome evaluation and (6) the most appropriate function for RC is to facilitate communication among evaluators, public decision makers, providers and the public. In the absence of a 'gold standard' or consensus, it is recommended the only RC be used in outcome evaluation, in the near future, in order to enhance comparability of change rate data among different studies.