The Iranian SF-12 Health Survey Version 2 (SF-12v2): Factorial and Convergent Validity, Internal Consistency and Test-Retest in a Healthy Sample

Objectives: Within the context of Health-Related Quality of Life studies, it was necessary to translate and evaluate the psychometric properties of the SF-12 Health Survey version 2. The aim of this study was to investigate the factorial structure, convergent validity and reliability of this instrument in a healthy Iranian sample, following translation and establishment of content and face validity. Methods: In this cross-sectional study the translated instrument was administered together with the Sense of Coherence Scale and Health Index in a convenience sample of healthy people (n=289) aged 18 to 76 years old between June and September 2006. A test-retest was conducted one month later. Results: Content Validity Index for Scale (85.6%) and face validity of the instrument were acceptable. The results of Exploratory Factor Analysis and Structural Equation Modeling by four models verified the existing two-factor structure, a physical and a mental component summary. All models exceeded the goodness of fit indices and showed a resemblance with the original instrument, except for models 3 and 4 (allowing cross-loadings). Although in these two models the General Health item and scale was loaded to the mental component rather than the physical component, construct validity of the instrument was confirmed. Also, physical and mental component summaries were significantly (P<0.001) correlated to the Sense of Coherence Scale (r=0.27, r=0.68) and Health Index (r=0.49, r=0.67). Cronbach’s alpha values and the intra-class correlation coefficients were ≥0.70 and ≥0.60, respectively. Discussion: The Iranian SF-12 Health Survey version 2 was a psychometrically sound instrument, implying that it is suitable for use with large-scale surveys in Iranian population, both in clinical and rehabilitation settings or at a public level.