Methodological approaches for assessing response shift in longitudinal health-related quality-of-life research

The impact of health state changes on an individual's quality of life (QOL) has gained increased attention in social and medical clinical research. An emerging construct of relevance to this line of investigation is response shift phenomenon. This construct refers to the changes in internal standards, in values, or in the conceptualization of QOL which are catalyzed by health state changes. In an effort to stimulate research on response shift, we present methodological considerations and promising assessment approaches for measuring it in observational and interventional clinical research. We describe and evaluate individualized methods, preference-based methods, successive comparison methods, design approaches, statistical approaches and qualitative approaches. The hierarchical structure of the construct is also discussed, with particular emphasis on how it might be elucidated by empirical assessment which uses the proposed methods and approaches. It is also recommended that criterion measures of change be included in future studies of response shift.