Responsiveness of SF-36 Health Survey and Patient Generated Index in people with chronic knee pain commenced on oral analgesia: analysis of data from a randomised controlled clinical trial
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(1) To assess the responsiveness of the Short Form 36 Health Survey (SF-36) and Patient Generated Index (PGI) in people with knee pain who were given oral analgesics; and (2) to perform content analysis of the SF-36 and PGI aiming to identify differences between the instruments and causes of different responsiveness.
An observational study nested within a randomised controlled trial comparing oral paracetamol, ibuprofen or a combination of the two in 884 community-derived people with chronic knee pain. Each participant was given the SF-36 and PGI questionnaires to fill out at baseline, day 10, week 7 and week 13 after commencement on analgesia. Responsiveness was measured as a standardised response mean from baseline, and contents of the instruments were analysed.
The PGI showed the greater responsiveness to analgesics than the SF-36 throughout the study period. Only the Bodily Pain Score of the SF-36 showed comparable responsiveness to the PGI. The standardised response mean of the PGI at 13 weeks was 0.61 (95% CI 0.51–0.72), and that of the Bodily Pain Score of the SF-36 was 0.49 (95% CI 0.39–0.58). Content analysis of the PGI identified multiple areas which are not represented in the SF-36 which may help explain its performance.
Overall the PGI is more responsive than the SF-36 to commonly used oral analgesics taken for knee pain. The PGI is able to elicit areas of individualised health-related quality of life which are not captured by the SF-36.
KeywordsKnee pain Osteoarthritis SF-36 Patient Generated Index Responsiveness Health-related quality of life
The authors are grateful to Reckitt Benckiser Healthcare International Ltd for financial support for the initial RCT and to the other investigators and research nurses involved in the trial which generated the data analysed in the present study.
There is no specific grant associated with this study. Reckitt Benckiser Healthcare International Ltd funded the original randomised controlled trial which provided the data for analysis, but the conception and design of the current nested study were undertaken independently to the funder with their approval.
Compliance with ethical standards
Conflicts of interest
The authors declare no conflicts of interest.
All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards.
Informed consent was obtained from all individual participants included in the study.
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