The construct validity and responsiveness of the EQ-5D, SF-6D and Diabetes Health Profile-18 in type 2 diabetes

Interest in the measurement of health related quality of life and psychosocial functioning from the patient's perspective in diabetes mellitus has grown in recent years. The aim of this study is to investigate the psychometric performance of and agreement between the generic EQ-5D and SF-6D and diabetes specific DHP-18 in Type 2 diabetes. This will support the future use of the measures by providing further evidence regarding their psychometric properties and the conceptual overlap between the instruments. The results will inform whether the measures can be used with confidence alongside each other to provide a more holistic profile of people with Type 2 diabetes.

A large longitudinal dataset (n = 1,184) of people with Type 2 diabetes was used for the analysis. Convergent validity was tested by examining correlations between the measures. Known group validity was tested across a range of clinical and diabetes severity indicators using ANOVA and effect size statistics. Agreement was examined using Bland-Altman plots. Responsiveness was tested by examining floor and ceiling effects and standardised response means.

Correlations between the measures indicates that there is overlap in the constructs assessed (with correlations between 0.1 and 0.7 reported), but there is some level of divergence between the generic and condition specific instruments. Known group validity was generally good but was not consistent across all indicators included (with effect sizes from 0 to 0.74 reported). The EQ-5D and SF-6D displayed a high level of agreement, but there was some disagreement between the generic measures and the DHP-18 dimensions across the severity range. Responsiveness was higher in those who self-reported change in health (SRMs between 0.06 and 0.25).

The psychometric assessment of the relationship between the EQ-5D, SF-6D and DHP-18 shows that all have a level of validity for use in Type 2 diabetes. This suggests that the measures can be used alongside each other to provide a more holistic assessment of with the quality of life impacts of Type 2 diabetes.