The Swedish RAND-36 Health Survey - reliability and responsiveness assessed in patient populations using Svensson’s method for paired ordinal data

Background: The Short Form 36-Item Survey is one of the most commonly used instruments for assessing health-related quality of life. Two identical versions of the original instrument are currently available: the public domain, license free RAND-36 and the commercial SF-36. RAND-36 is not available in Swedish. The purpose of this study was threefold: to translate and culturally adapt the RAND-36 into Swedish; to evaluate its reliability and responsiveness using Svensson’s method for paired ordered categorical data; and to assess the usability of an electronic version of the questionnaire. The translation process included forward and backward translations and reconciliation. Test-retest reliability was examined during a period of two-weeks in 84 patients undergoing dialysis for chronic kidney disease. Responsiveness was examined in 97 patients before and 2 months after a cardiac rehabilitation program. Usability tests and cognitive debriefing of the electronic questionnaire were carried out with 18 patients. Results: The Swedish translation of the RAND-36 was conceptually equivalent to the English version. Test-retest reliability was supported by non-significant relative position (RP) values among dialysis patients for all RAND-36 subscales (range − 0.02 to 0.10; all confidence intervals (CI) included zero). Responsiveness was demonstrated by significant improvements in RP values among cardiac rehabilitation patients for all subscales (range 0.22–0.36; lower limits of all CI > 0.1) except two subscales (General health, RP -0.02; CI -0.13 to 0.10; and Role functioning/emotional, RP 0.03; CI -0.09 to 0.16). In cardiac rehabilitation patients, sizable individual variation (RV > 0.2) was also shown for the Pain, Energy/fatigue and Social functioning subscales. The electronic version of RAND-36 was found easy and intuitive to use. Conclusions: Our results provide evidence supporting the reliability and responsiveness of the newly translated Swedish RAND-36 and the user-friendliness of the electronic version. Svensson’s method for paired ordinal data was able to characterize not only the direction and size of differences among the patients’ responses at different time points but also variations in response patterns within groups. The method is therefore, besides being suitable for ordinal data, also an important and novel tool for gaining insights into patients’ response patterns to treatment or interventions, thus informing individualized care.