Validation of the Quality of Life and Function Five Domain Scale (QFS-5) against the EuroQol-5D (EQ-5D)

INTRODUCTION: Quality of life (QoL) captures objective life conditions, subjective wellbeing, and personal aspirations. There is growing interest in ability-based, patient-centred instruments that are not confounded by health outcomes. The Quality of Life and Function Five Domain Scale (QFS-5) applies a multi-dimensional approach to measurement of QoL with a focus on abilities and life engagement. METHODS: The QFS-5 was validated in 1610 participants aged ≥ 50 from the Canadian Platform for Research Online to Investigate Health, Quality of Life, Cognition, Behaviour, Function, and Caregiving in Aging (CAN-PROTECT). Internal consistency was assessed using Cronbach′s alpha and item-total correlations. Confirmatory factor analysis (CFA) evaluated domain structure. Criterion validity was tested through Pearson′s correlation with the EuroQol-5D (EQ-5D). Convergent and discriminant validity were evaluated from associations with cognitive, mental health, and functional measures. Floor and ceiling effects were investigated. RESULTS: The QFS-5 demonstrated excellent internal consistency ( α = 0.92); CFA supported the proposed domain structure with strong item loadings. Criterion validity was confirmed with correlation of -0.61 against the EQ-5D; higher symptom burden on related scales were associated with lower QFS-5 scores. Floor effects were minimal, while modest ceiling effects were observed in some domains. No significant floor or ceiling effects were found in participants living with frailty. CONCLUSION: The QFS-5 establishes validity, reliability, and effective use of an ability-based domain structure within a sample of mostly cognitively unimpaired, community-dwelling older adults. The QFS-5 aligns with EQ-5D measurements, demonstrating its potential utility in research and clinical practice to measure relevant patient reported QoL outcomes.