Interpreting change scores of tests and measures used in physical therapy.

Over the past decade, the methods and science used to describe changes in outcomes of physical therapy services have become more refined. Recently, emphasis has been placed not only on changes beyond expected measurement error, but also on the identification of changes that make a real difference in the lives of patients and families. This article will highlight a case example of how to determine and interpret "clinically significant change" from both of these perspectives. The authors also examine how to use item maps within an item response theory model to enhance the interpretation of change at a content level. Recommendations are provided for physical therapists who are interpreting changes in the context of clinical practice, case reports, and intervention research. These recommendations include a greater application of indexes that help interpret the meaning of clinically significant change to multiple clinical, research, consumer, and payer communities.