Comparing multi-attribute utility instruments: CP-6D, a Cerebral palsy specific instrument, vs AQoL-4D

Abstract

BACKGROUND: Economic-evaluations of Cerebral palsy (CP) were based on utility estimates of health-related quality of life (HRQoL) from generic multi-attribute utility instruments (MAUIs). However, generic instruments had limited use as they could not capture some of the important aspects of living with CP. The Cerebral palsy 6 Dimension (CP-6D) is a disease specific MAUI. In this study, we compared the results of CP-6D with the Assessment of Quality of Life (AQoL-4D), a generic MAUI, and tested the criterion validity of the CP-6D in the general population. METHODS: An online survey of the Australian general population (n=2002), who completed both the AQoL-4D and CP-6D MAUIs, was conducted. Validity was assessed from the correlations between the domains, items and instruments. ANOVA and t-tests were used to assess the instrument's discrimination in different social demographic categories. RESULTS: There was a moderate correlation between the instruments (0.64). Differences in socio-demographic characteristics showed a medium effect size (p <0.001) in both instruments and had a similar effect on utility weights in both instruments. Although, the CP-6D was more sensitive to changes in income and education. CONCLUSIONS: Our results suggest that CP-6D and AQoL-4D were measuring a similar underlying construct. Both instruments responded similarly to socio-demographic differences.