EQ-5D in patients with dementia: an investigation of inter-rater agreement

BACKGROUND: There are difficulties in obtaining health-related quality of life (HRQL) data from patients with dementia due to variation in their cognitive ability, degree of insight and capacity to make judgments. The use of proxies is one solution. OBJECTIVES: To examine the inter-rater agreement of patient and proxy completion of the EuroQol EQ-5D instrument (EQ-5D). RESEARCH DESIGN: The EQ-5D instrument was completed separately by patients, their caregivers and a physician. Assessment of inter-rater agreement involved comparison of self-completed (patient) and proxy-completed (caregiver and physician) responses for each dimension of EQ-5D, using a weighted kappa score. Three key hypotheses were tested. (1) Interrater agreement would be stronger between patient and caregiver than between patient and physician. (2) Interrater agreement would be stronger on the 'observable' and objective dimensions of EQ-5D. (3) Interrater agreement between patient and proxies would be stronger for patients with earlier dementia. SUBJECTS: The sample comprised 64 patients with a range of dementia severity. MEASURES: The EQ-5D health state classification system and visual analogue scale were used to assess HRQL. Global severity of dementia was determined using the Clinical Dementia Rating Scale. RESULTS: The principal finding of this study was that responses to EQ-5D questions were highly variable across the three raters such that none of the three hypotheses were strongly supported. CONCLUSIONS: The data provide some support for the use of EQ-5D when interviewer administered. However, there are serious concerns regarding the validity of patient self-rated HRQL data obtained in this study and uncertainty exists regarding who the appropriate proxy should be, as different groups of proxies provide different results. It was not clear whether caregivers or physicians represent better proxies. Further research should focus on the comparison of caregivers and physicians as proxies.