The measurement and analysis of change plays a central role in many areas of clinical research. It would be difficult to provide an exhaustive list of clinical research endeavors in which this process is central. Many problems associated with the measurement and analysis of change are common to all such endeavors, including areas as diverse as examining the effectiveness of treatments for specific behavioral disorders, investigating developmental outcomes in impaired pediatric or adult populations, or identifying cognitive and emotional sequellae of acquired disorders. All these areas present researchers with difficult questions concerning the measurement and analysis of change. Ironically, some of these questions have been made