Difference Scores: Rationale, Formulation, and Interpretation

Despite decades of use, the appropriateness of different scores for estimating discrepancies between measurement units continues to be a source of much debate. John Tisak and Carlla S. Smith conclude their position by proposing alternative approaches to conceptualizing difference scores, but methods that maintain the scores' essential character. Jeffrey R. Edwards responds to points raised by Tisak and Smith, arguing the merits of his regression-based procedure for testing response surfaces, and proposing that the use of difference scores be abandoned. Tisak and Smith comment on Edwards' proposal.