Diabetes-specific or generic measures for health-related quality of life? Evidence from psychometric validation of the D-39 and SF-36.

OBJECTIVE: There is a debate regarding the use of disease-specific versus generic instruments for health-related quality of life (HRQOL) measures. We tested the psychometric properties of HRQOL measures using the Diabetes-39 (D-39) and the Medical Outcomes Study 36-Item Short-Form Health Survey (SF-36).
METHODS: This was a cross-sectional study collecting data from 280 patients in Taiwan. Exploratory factor analysis was conducted to evaluate construct validity of the two instruments. Known-groups validity was examined using laboratory indicators (fasting, 2-hour postprandial plasma glucose, and hemoglobin A1c), presence of diabetic complications (retinopathy, nephropathy, neuropathy, diabetic foot disorder, cardiovascular and cerebrovascular disorders), and psychosocial variables (sense of well-being and self-reported diabetes severity). Overall discriminative power of the two instruments was evaluated using the C-statistic.
RESULTS: Three distinct factors were extracted through factor analysis. These factors tapped all subscales of the D-39, fourphysical subscales of the SF-36, and four mental subscales of the SF-36, respectively. Compared with the SF-36, the D-39 demonstrated superior known-groups validity for 2-hour postprandial plasma glucose groups but was inferior for complication groups. Compared with the SF-36, the D-39 discriminated better between self-reported severity known groups, but was inferior between well-being groups. In overall discriminative power, the D-39 discriminated better between laboratory known groups. The SF-36, however, was superior in discriminating between complication known groups.
CONCLUSIONS: For psychometric properties, the D-39 and the SF-36 were superior to each other in different regards. The combined use of a disease-specific instrument and a generic instrument may be a useful strategy for diabetes HRQOL assessment.