How useful are the SF-36 sub-scales in older XXXX ? Mokken scaling of data from the HALCyon programme.

@entity1 @entity1032
PURPOSE: To evaluate two psychometric properties of SF-36, namely unidimensionality and reliability. METHODS: The data are from three cohorts in the HALCyon collaborative research programme into healthy ageing: Aberdeen Birth Cohort 1936 (n  =  428), Hertfordshire Ageing Study (n  =  358) and Hertfordshire Cohort Study (n  =  3,216). The Mokken scaling model was applied to each sub-scale of SF-36 to evaluate unidimensionality as indicated by scalability. The lower bound for internal consistency reliability was determined by Cronbach's alpha. RESULTS: All six sub-scales of SF-36, with the exception of general health (GH) and @entity1032 ( @entity1032 ), demonstrated strong scalability (0.5   <=  H  <  1). The results were consistent across all 3 cohorts. Both GH and @entity1032 showed medium scalability (0.4   <=  H  <0.55), although individual items 'sick easier..', 'as healthy as..' and 'expect to get worse' of the GH sub-scale and 'nervous', 'happy' in the @entity1032 sub-scale had low scalability (H  <  0.4) in the oldest cohort (aged 73-83). Cronbach's alphas for all sub-scales were between 0.70 and 0.92. CONCLUSIONS: The unidimensionality and reliability of the sub-scales of SF-36 are sufficient to make this a useful measure of health-related quality of life in older @entity1 . Caution is needed when interpreting the results for GH and @entity1032 in the oldest cohort due to the poor unidimensionality.
