Objectives: Quality of Life (QOL) is considered an important outcome measure in the evaluation of palliative treatment. Observed QOL in seriously ill patients often does not show the expected deterioration. These contradictory findings highlight the importance of studying response shift in QOL. Schwartz & Sprangers (2000) suggest: Comparison of pre- and then-test could provide indications of change in internal standards; SEIQOL-DW allows respondents to "define" their individual QOL by nominating the five most important aspects of their life ("elicited cues") and by indicating the relative contribution ("weight") of each of these to their overall QOL. At different points in time, patients might nominate different "cues" (reconceptualization) and might change their weighting of identical "cues" (value change). We tested the usefulness of a "then-test" approach and SEIQOLDW for measuring response shift.
Methods: A qualitative exploratory longitudinal multiple case study (N-31); EORTC QLQ-C30 and QLQ-LC13; then-test; SEIQOL-DW; Three- Step Test-Interview (consisting of observation with think aloud, focused debriefing and semi-structured interviewing); audio recordings and transcripts.
Results: Results of the then-test suggested changes in internal standards, but interview transcripts showed that these were mainly artifacts caused by recall problems and interpretative variance that cannot be considered response shift. SEIQOL generated evidence of response shift but comparison with interview data showed that there were instances of "false positives" (no response shift although SEIQOL data suggested that there was) and "false negatives" (response shift that was not observed through SEIQOL).
Conclusion: The then-test does not provide a reliable measurement of response shift. SEIQOL-DW is a useful instrument for eliciting evidence of response shift that needs to be further explored in complementary in-depth interviews.