Background. Intuitively, health and capability are distinct but linked concepts. This study aimed to quantify the link between a measure of health status (EQ-5D-3L) and capability (ICECAP-O) using regression-based methods.
Methods. EQ-5D-3L and ICECAP-O data were collected from a sample of older people (n=584), aged over 65-years, requiring a hospital visit and/or care home resident, and recruited to one of three studies forming the Medical Crisis in Older People (MCOP) programme in England. The link of EQ-5D-3L with: ICECAP-O tariff scores were estimated using ordinary least squares (OLS) or censored least absolute deviation (CLAD) regression models; ICECAP-O domain scores was estimated using multinomial logistic (MNL) regression. Mean Absolute Error (MAE), Root Mean Squared Error (RMSE), absolute difference (AD) between mean observed and estimated values, and the R2 statistic were used to judge model performance.
Results. In this sample of older people (n=584), higher scores on the EQ-5D-3L were shown to be linked with higher ICECAP-O scores when using linear regression. An OLS-regression model was identified to be the best performing model with the lowest error statistics (AD = 0.0000; MAE = 0.1208; MSE = 0.1626) and highest goodness of fit (R2 = 0.3532); model performance was poor when predicting the lower ICECAP-O tariff scores. Three domains of the EQ-5D-3L showing a statistically significant quantifiable link with the ICECAP-O tariff score were self-care, usual-activities, and anxiety/depression.
Conclusion. A quantifiable, but weak, link between health (EQ-5D-3L) and capability (ICECAP-O) was identified. The findings from this study add further support that the ICECAP-O is providing complimentary information to the EQ-5D-3L. Mapping between the two measures is not advisable and the measures should not be used as direct substitutes to capture the impact of interventions in economic evaluations.