Utility and Validity of the Self-administered SF-36: Findings From an Older Population

Abstract

Introduction: The objectives of this study were to assess the utility and validity of the self-administered SF-36 and the effect of visual or cognitive impairment on these measures in an older population. Materials and Methods: Attempt rates, completion rates and internal consistency (Cronbach α) were compared within the second cross-sectional, population-based Blue Mountains Eye Study (n = 3509, mean age 66.7 years, 57% women). Results: The SF-36 was attempted by 3162 (90.1%) participants, of which 2470 (78.1%) completed all items and 2873 (90.9%) completed sufficient items for calculation of all dimensions. In a multivariate model adjusting for age, sex, and presenting visual and cognitive impairments, women (P = 0.011) and participants with visual or cognitive impairments (P<0.0001) were less likely to attempt the questionnaire. Completion rates were significantly lower with increasing age (P <0.0001), in men (P ≤0.0005) and in those with cognitive impairment (P <0.0001). A high level of internal consistency (Cronbach α >0.85 for all dimensions) and construct validity was demonstrated, the latter distinguishing between those with and without medical conditions, disabilities or recent hospital admissions (P <0.01). As the prevalence of visual or cognitive impairment was relatively low in this population, we found no apparent effect of these impairments on the validity of SF-36. Conclusions: Attempt and completion rates, but not internal consistency and construct validity, of the SF-36 were influenced by age, gender, and presenting visual and cognitive impairments. The overall high attempt and completion rates, internal consistency and construct validity suggest that the self-administered SF-36 is a suitable health-related quality of life (HRQOL) measure in similar older community-living populations. Key words: Blood amino acid, Normal ranges, Reference values, Urine amino acids