Purpose: Due to their cognitive impairment, the health-related quality of life (HRQoL) of patients with dementia is often rated by proxies. This study aims to analyse the psychometric properties of the EQ-5D applied to patients with mild to moderate dementia and their family caregivers.
Methods: Three hundred and ninety patients and their caregivers were asked to assess the patients' HRQoL using the EQ-5D. The German population-based time trade-off values were used to calculate utility weights. Acceptance, discriminative ability, construct validity, inter-rater agreement and responsiveness were tested. Factors that could have an impact on inter-rater agreement were analysed using a multivariate regression.
Results: Five per cent of patients did not fill out the EQ-5D. The response rate of caregivers and of patients with mild dementia was higher than that of patients with moderate dementia. There were no floor or ceiling effects. The test results of the caregivers concerning construct validity and responsiveness were better than those of the patients. The inter-rater reliability was not satisfactory either on the dimension level or on the utility score level. Caregivers gave the patients' HRQoL significantly lower ratings than did the patients themselves. Better abilities of the patient to perform activities of daily living and a lower subjective burden of the caregiver were associated with a higher inter-rater agreement.
Conclusions: The study showed that the EQ-5D is especially applicable to patients with mild dementia and their caregivers as proxies. However, there are important differences between patient and proxy ratings, even in cases of mild dementia, at the dimension level as well as utility score level, which should be considered in the interpretation of quality of life scores.