Purpose: This study examined the underlying factor structure of health-related quality of life (HRQoL) domains across five preference-weighted indexes of HRQoL: SF-6D, EQ-5D, HUI2, HUI3 and QWB-SA.
Method: Data came from the National Health Measurement Study (NHMS) a telephone survey of a nationally representative sample of 3844 non-institutionalized adults aged 35-89 residing in the continental US conducted in 2005-06. Data for all five indexes were collected from each survey respondent and arrayed as categorical scores for each domain included in each index (e.g., EQ-5D has 5 domain scores with 3 categories each). We used oblique categorical exploratory factor analysis to explore the underlying dimensions of these data while accounting for the complex survey design of the NHMS. Confirmatory factor analysis was used to assess model fit. Item response theory was applied to explore the amount of information HRQoL domains contribute across the continuum of the underlying latent dimensions.
Result: The first 3 eigenvalues (13.7, 2.2, 1.7) were greater than one, hence 3 main dimensions of HRQoL domains were identified: “physical function,” “psychosocial function” and “pain.” Fourteen out of 26 HRQoL domains contributed to the physical dimension, and 6 domains contributed to each of the other two dimensions. The 3 dimensions were correlated: 0.42 (physical, psychosocial), 0.54 (physical, pain), 0.43 (psychosocial, pain). Average loading on the physical dimension was 0.71 with smallest being 0.26 (HUI3 Hearing) and largest 0.91 (QWB-SA Physical Activity). On the psychosocial dimension, the average loading was 0.77 with smallest 0.59 (HUI3 Cognition) and largest 0.90 (SF-6D Social Function). Average loading on the pain dimension was 0.82; although primarily defined by pain domains, extreme loadings on this factor were 0.62 (SF-6D Vitality) and 0.94 (EQ-5D Usual Activities). This factor structure fit the HRQoL data well (CFI = 0.97, TLI = 0.98, RMSEA = 0.045).
Conclusion: Collectively, HRQoL domains of five commonly-used HRQoL indexes capture 3 underlying latent dimensions of HRQoL, physical and psychosocial function and pain. Some HRQoL domains, in particular domains of sensation on HUI3 (Hearing, Speech, Vision), SF-6D Vitality, and HUI3 Cognition, displayed relatively more unique variance not captured by the 3 main identified dimensions. HRQoL domains contributed most information at the lower to middle range of the latent continuum of dimensions and least information at the high end.
Candidate for the Lee B. Lusted Student Prize Competition