The Swedish SF-36 Health Survey--I. Evaluation of data quality, scaling assumptions, reliability and construct validity across general populations in Sweden

Abstract

We document the applicability of the SF-36 Health Survey, which was translated into Swedish using methods later adopted by the International Quality of Life Assessment (IQOLA) Project procedures. To test its appropriateness for use in Sweden, it was administered through mail-out/mail-back questionnaires in seven general population studies with an average response rate of 68%. The 8930 respondents varied by gender (48.2% men), age (range 15-93 years, mean age 42.7), marital status, education, socio-economic status, and geographical area. Psychometric methods used in the evaluation of the SF-36 in the U.S. were replicated. Over 90% of respondents had complete items for each of the eight SF-36 scales, although more missing data were observed for subjects 75 years and over. Scale scores could be computed for the vast majority of respondents (95% and over); slightly fewer in the oldest subgroup. Item-internal consistency was consistently high across socio-demographic subgroups and the eight scales. Most reliability estimates exceeded the 0.80 level. The highest reliability was observed for the Bodily Pain Scale where all subgroups met the 0.90 level recommended for individual comparisons; coefficients at or above 0.90 were also observed in most subgroups for the Physical Functioning Scale. Tests of scaling assumptions including hypothesized item groupings, which reflect the construct validity of scales, were consistently favorable across subgroups, although lower rates were noted in the oldest age group. In conclusion, these studies have yielded empirical evidence supporting the feasibility of a non-English language reproduction of the SF-36 Health Survey. The Swedish SF-36 is ready for further evaluation.