Medical outcomes study short form 36: Testing and cross-validating a second-order factorial structure for health system employees

  • 1 December 1998
    • journal article
    • research article
    • Vol. 33  (5) , 1361-1380
Abstract
Objective. To test the factorial validity of the SF-36. Data Source. Sample data collected in 1995 and 1996 using telephone interviews with health system employees as part of a study of health status. Methods of Analysis. Confirmatory factor analysis and structural equation modeling techniques were used to evaluate the data. Principal Findings. The results of this study suggest that (1) Mental Health and Physical Health are not independent; (b) Mental Health cross-loads onto Physical Health; (c) general health loads onto Mental Health instead of Physical Health; (d) many of the error terms are correlated; (e) the physical function subscale is not reliable across the samples or the "age" or "education" subgroups; and (f) the mental health subscale path from Mental Health is not reliable across some subgroups. This hierarchical factor pattern was replicated across both samples. Conclusions. This study supports the second-order factorial structure of the SF-36. Adding the covariance path between the variables Physical Health and Mental Health improved model fit. Two paths from the second-order latent variables to the first-order latent variables differ from the original hypothesized structure of the SF-36. Health perception was influenced by Mental Health rather than Physical Health, and mental health was influenced by both Mental Health and Physical Health. This cross-loading suggests that the perception of Physical Health greatly affects mental health. Scale instabilities in the SF-36 across subgroups suggest that a comparison of mean scores or summary scores is inappropriate. Data interpretation can be improved if multigroups structural equation modeling is used.