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.