Aims: When individuals experience changes in their health states, they may alter their internal standards, values, or conceptualization of quality of life (QOL). Such 'response shifts' can affect or distort QOL outcome measurement, which is of particular concern when evaluating medical or psychosocial interventions. Although clinicians and researchers acknowledge the occurrence of response shifts, little is known about the magnitude and clinical significance of those effects. To fill this gap in knowledge about response shift phenomena, we performed a meta-analysis on published QOL articles on response shift.
Methods: Extensive literature searches and multiple contacts with researchers yielded a collection of 494 articles for potential reviewing. We retained only published longitudinal studies that measured response shift, resulting in 26, of which 19 reported the requisite data for computing an effect size (ES). We calculated and compared the ESs for each study with regard to potential moderator variables: the QOL domains measured, disease group investigated, sample size, and response shift method used. We rated studies for quality to allow ES weighting.
Results: When we examined ES absolute values, we found that ES magnitude was small, with the largest ESs detected for fatigue, followed by global QOL, physical role limitation, psychological well-being, and pain (mean absolute value(ES(weighted)) = 0.32, 0.30, 0.24, 0.12, and 0.08, respectively). ESs varied considerably in direction. Aggregating raw ES scores over all studies led to positive and negative values canceling each other out (mean directional ES(weighted) = 0.17, 0.02, -0.01, 0.06, and 0.02, respectively). We found little evidence of an effect for the moderator variables examined.
Conclusions: A definitive conclusion on the clinical significance of response shift cannot currently be drawn from existing studies. For a number of reasons, ES estimates were primarily based on then-test results, a method that is not without criticism, such as its susceptibility to recall bias. We recommend a standardized approach for reporting results of future response shift research to advance the field and to facilitate interpretation and comparisons across studies.