response shift in measuring health-related quality of life as pertaining to health: concepts, definitions, and challenges

as a major consequence of medical interventions, quality of life (qol) is of great importance for patients suffering from refractory diseases, particularly cancer. the unbiased measurement of changes in qol is thus crucial in such cases. a prevalent bias related to qol research is the ‘response shift’ (rs) phenomenon. this review article aims to define rs and the challenges in measuring it. in addition, it addresses the methodological approaches used to measure this bias in observational and clinical studies. response shift refers to changes in one’s health condition as a result of changes in the meaning of one’s self-evaluation. these changes result when the patient faces his/her new conditions and may be reflected as greater as or smaller than they actually are. the present article describes the individualized methods, the preference-based methods, the structural equation modeling and the then-test method used for evaluating rs, and discusses their applications. finally, by comparing these methods, it concludes that the simplest and most efficient approach for evaluating rs is the then-test approach. by emphasizing that these methods should be applied in clinical studies, the present article describes the most important methods for evaluating rs. the effect of rs has been neglected in the majority of qol studies. we therefore recommend taking into account the effect of rs in the interpretation of qol changes in longitudinal studies.