Applications of response shift theory and methods to participation measurement: a brief history of a young field

Measurement of participation in people with disability can pose psychometric and conceptual challenges. Ambiguous or paradoxical findings can occur because of differences among people or changes within people regarding internal standards, values, or conceptualization of participation. These response shifts can affect standard psychometric indices, such as reliability and validity. We focus herein on the interpretation of patient-reported outcomes and, in particular, on the cognitive appraisal processes known as response shift. We present theoretical and conceptual distinctions building on response shift theory and other current developments in health-related quality of life research to inform participation measurement research. We discuss how response shifts can influence the interpretation of reliability, validity, and responsiveness of participation measures. We then discuss the evidence for the clinical significance of response shift phenomena and describe current design, statistical, and individualized approaches for detecting response shift phenomena.