Response shift influenced estimates of change in health-related quality of life poststroke

The interpretability of changes in perceived health status over time is threatened if people experience a response shift. This study assessed whether the recovery process following stroke altered individuals' perceptions of past health status and the impact that change in internal standards (response shift) had on ratings over time. We hypothesized that individuals with stroke would experience changes in internal standards, not experienced by the control group. Two other hypotheses related to objective criterion measures also were tested.

Individuals were recruited through a randomized trial of acute poststroke care. Health status was evaluated at baseline (within the first week poststroke), 6 and 24 weeks later using the EQ VAS. At 6 and 24 weeks, subjects were asked to retrospectively re-evaluate their health status for the preceding evaluation using the then test technique.

The pattern of mean scores was indicative of changes in internal standards among individuals with stroke but not for the control group. Memory had an impact on estimates of response shift. Hypotheses related to the objective criterion measures were not supported.

The results suggest that there was a change in internal standards, and that measures of improvement in health status are different based on prospective as compared to retrospective ratings. Further understanding of the impact of recall on the assessment of response shift using the then test is needed to validate the use of this technique.