Measurement invariance and differential item functioning of a care staff proxy measure of nursing home resident dementia-specific quality of life (DEMQOL-CH): do care aides' first language, and care aides' and residents’ ethno-cultural background matter?

Quality of life (QoL) is a priority goal of dementia care, but measuring QoL becomes increasingly difficult as a person's ability to self-report declines. QoL measurement is particularly challenging among Nursing home (NH) residents, due to their often advanced cognitive impairment. The DEMQOL-CH is a validated tool to assess NH residents' QoL, using care staff proxy reports. Care staff and residents often have diverse ethno-cultural backgrounds, which may affect the measurement of QoL. Our objective was to assess measurement invariance and differential item functioning (DIF) of the DEMQOL-CH based on care staff ethno-cultural background, language, and resident ethno-cultural background. In a convenience sample of 9 NHs in the Canadian province of Alberta, research assistants conducted structured interviews with 119 care staff between July and September 2021 to complete DEMQOL-CH assessments of 612 residents. We performed confirmatory factor analyses, multiple group item response theory analyses, and DIF analyses. Measurement of the overall DEMQOL-CH score was affected by care staff ethno-cultural background and language (lack of scalar measurement invariance), but not by resident ethno-cultural background. Six of the 31 DEMQOL-CH items had DIF based on both, care staff ethno-cultural background and language, 2 items had DIF based on care staff ethno-cultural background, 4 items had DIF based on care staff language. Resident ethno-cultural background did not lead to DIF. The lack of measurement invariance and the presence of DIF affects the comparability of DEMQOL-CH assessments collected from care staff with diverse ethno-cultural and/or language backgrounds. However, the extent of the issues identified is small and the tool's other psychometric properties are robust. Therefore, we suggest that it is reasonable to continue to use the DEMQOL-CH in its current form, with careful consideration of methods to deal with and adjust for measurement invariance.