Quality of life measurement after stroke - Uses and abuses of the SF-36

Background and Purpose-The Medical Outcomes Study 36-item Short-Form Health Survey (SF-36) is widely used to measure health status after stroke. However, a fundamental assumption for its valid use after stroke has not been comprehensively tested: is it legitimate to generate scores for 8 scales and 2 summary measures using the standard algorithms? We tested this assumption. Methods-SF-36 data from 177 people after stroke were examined (71% male; mean age, 62). We tested 6 scaling criteria to determine the legitimacy of generating the 8 SF-36 scale scores using Likert's method of summed ratings, and we tested 2 scaling criteria to determine the appropriateness of the standard SF-36 algorithms for weighting and combining scale scores to generate 2 summary measures (physical and mental). Results-Scaling assumption, were fully satisfied for 6 of the 8 scales, but 3 of these 6 scales had notable floor and/or ceiling effects. Assumptions for generating 2 SF-36 summary measures were not satisfied. Conclusions-In this sample, 5 of the 8 SF-36 scales had limited validity as outcome measures after stroke, and the reporting of physical and mental summary scores was not supported. Results raise questions about the use of the SF-36 in stroke, and the SF-12 that is developed from it, and highlight the importance of testing scaling assumptions when applying existing scales to new populations.