Impact of response shift on longitudinal quality-of-life assessment in cancer clinical trials.

The assessment of longitudinal change in subjective patient-reported outcomes such as health-related quality of life (HRQoL) is a key component of many clinical and research evaluations. A major goal of measuring patient-reported HRQoL is to determine to what extent changes in HRQoL reports over time represent true changes in HRQoL due to treatment or cancer and to what extent they reflect measurement error. Indeed, the subjective assessment of HRQoL change is subject to response-shift effects, whereby health changes lead to shifts in internal standards (i.e., 'recalibration'), values (i.e., 'reprioritization') and conceptualization (i.e., 'reconceptualization') of key HRQoL domains. Response shift is a naturally occurring process that could distort the interpretation of change in HRQoL scores over time in interventional studies. Assessing response shift may therefore be needed to obtain a valid and sensitive assessment of change over time. Several methods to detect and measure the size and the direction of response shift are available. In this article, we summarize the methods used to assess and adjust for the response-shift effect in clinical trials. Nevertheless, our understanding of the parameters and processes associated with response shift is very limited. Further research is still needed to better understand how to measure the different components of response shift and how to take them into account in cancer research.