Background: Quality of life (QoL) in dementia is a complex construct and factors that predict QoL ratings are unclear. We designed this study to determine: (1) the agreement in QoL ratings between community-dwelling patients with mild to moderate dementia and family carers; and (2) the factors associated with self-reported and two types of carer-reported QoL ratings: carer–carer perspective and carer–patient perspective.

Methods: A cross-sectional study was carried out of 80 community-dwelling patients with the diagnosis of probable Alzheimer's disease (AD) of mild or moderate severity according to NINCDS-ADRD criteria, and their 80 family carers. The QoL-AD was the primary outcome measure. We collected patients’ self-reported QoL ratings and two types of carer-reported QoL ratings: carer–patient and carer–carer perspectives. Explanatory variables included demographics, lifestyle, and clinical information from patients and carers, along with cognition, awareness, psychopathology, burden-of-care, and functionality in daily life. Bland-Altman plots guided the interpretation of agreement by visualizing the distribution of all the ratings. Univariate and multivariate regression analyses were conducted to examine the contribution of candidate explanatory factors.

Results: Patients and their carers showed good agreement in their QoL ratings, although the total scores of carers (regardless of perspective) were lower than the scores of patients. Depression, insight and use of anti-dementia agents were associated with QoL self-ratings, whereas cognitive function was directly associated and depression inversely associated with carers’ QoL ratings.

Conclusion: Mild to moderate community-dwelling AD patients and their carers (with different perspectives) agree within an acceptable range in QoL ratings but the ratings are driven by different factors, and consequently are not interchangeable but complementary. They provide valuable information when used separately, not in a composite score.