Reliability and validity of the Japanese version of a self‐report (DEMQOL) and carer proxy (DEMQOL‐PROXY) measure of health‐related quality of life in people with dementia

AIM: The DEMQOL is a self-report measure of subjective quality of life of people with dementia, and the DEMQOL-PROXY is a carer proxy version. The study aimed to develop Japanese versions of the DEMQOL and DEMQOL-PROXY, and test their reliability and validity. METHODS: Translation, reverse translation and equivalency evaluation by the original author were used to develop Japanese versions of the DEMQOL (DEMQOL-J) and DEMQOL-PROXY (DEMQOL-PROXY-J). Interviews were carried out with 90 pairs of people with dementia and their carers to assess their quality of life using the DEMQOL-J, DEMQOL-PROXY-J and other quality of life scales. Internal consistency was evaluated using Cronbach's alpha. Test-retest reliabilities were evaluated using intraclass correlation coefficients. Criterion validity was determined using Pearson's correlation coefficient. RESULTS: Data from 87 pairs who completed the interviews were analyzed. Cronbach's alphas for the DEMQOL-J and DEMQOL-PROXY-J were 0.930 and 0.927, respectively. For 27 pairs who were re-interviewed, the intraclass correlation coefficients for the DEMQOL-J and DEMQOL-PROXY-J were 0.942 (P < 0.001) and 0.942 (P < 0.001), respectively. Both the DEMQOL-J and DEMQOL-PROXY-J correlated significantly with other quality of life scales (the Quality of Life - Alzheimer's Disease instrument, the EuroQol-5D-3L and the World Health Organization Well-Being Index-5-J; P < 0.001). There was also a significant correlation between the DEMQOL-J and the DEMQOL-PROXY-J (r = 0.645, P ≤ 0.001). CONCLUSIONS: The DEMQOL-J and DEMQOL-PROXY-J are reliable and valid measures of dementia-specific quality of life. Geriatr Gerontol Int 2019; 19: 487-491.