The Swedish RAND-36: psychometric characteristics and reference data from the Mid-Swed Health Survey
BACKGROUND: This study aims to evaluate data quality, scaling properties, and reliability of the Swedish RAND-36 in a general population sample and to present reference data for the Swedish population. METHODS: Testing of data quality, scaling assumptions and reliability followed methods recommended for the International Quality of Life Assessment Project, previously used for psychometric testing of SF-36 and RAND-36. Data were collected via regular mail for a random stratified sample of the general population in a Swedish county. Weighted means for RAND-36 scores were used and differences by sex, age, education, and occupational groups were tested. RESULTS: The response rate was 42%, and the sample comprised 3432 persons (45% men, 55% women) with a median age of 56.9 years. The internal consistency reliability was satisfactory, with Cronbach's alphas > 0.80 for all eight scales. The percentage of missing items was low, ranging between 1.3% and 3.2%. No floor effects (≥15%) were noted, while ceiling effects were observed for physical functioning, role-functioning/physical, pain, role-functioning/emotional, and social functioning. Item-scale correlations were satisfactory (r ≥ 0.40). Correlations among the physical health scales were strong (range 0.58-0.68) as were the correlations among the mental health scales (range 0.58-0.73). Men reported significantly better health-related quality of life (HRQoL) on all scales, although the gender differences were small. Comparisons among age groups showed approximately equal scores among those 20-29, 30-39, and 40-49 years, while significant decreases in physical health were observed in the older age groups. Substantially worse physical health scores were observed in the oldest age group (80+). Significant differences among age groups were noted also for the mental health scales; however, better energy/fatigue and emotional well-being scores were seen in the older age groups, except for the oldest (80+). Those with university education reported significantly better scores on all scales compared to those with mandatory education. CONCLUSIONS: The study suggests that the Swedish version of RAND-36 is an acceptable and reliable instrument for measuring HRQoL in the general population. The study provides reference data that can be used for norm-based comparisons.