OBJECTIVES: Conventional measurement systems used to estimate QALY, like the EQ-5D-5L, predominantly focus on health-related quality of life (HRQoL). One approach to expanding the health focused QALY is to merge descriptive systems that measure different QoL constructs into a unified instrument. In this paper we investigate the possibility of merging the EQ-5D-5L and the Adult Social Care Outcomes Toolkit (ASCOT) using classic psychometric analysis to explore the relationship between the instruments and assess them for complementarity.

METHODS: The study had a longitudinal design and data was collected via an online panel during May-July 2023. Australian adults aged 18 years and above were recruited. Those consenting to recontact also participated in a follow-up survey after 14 days. Psychometric assessments included ceiling and floor effects, Spearman correlation, one-way ANOVA, and Cohen’s D. Test-retest reliability was assessed using Cohen’s kappa.

RESULTS: In the analysis, 1505 baseline and 797 follow-up survey responses were included. Mean utility scores for EQ-5D-5L and ASCOT were 0.88 and 0.85, respectively. The EQ-5D-5L displayed evidence of a ceiling effect (23.3%). Most items across the instruments had poor correlation, with the highest observed correlation being between anxiety/depression and occupation (rho=0.41) and the lowest being between self-care and dignity (rho=0.11). Construct validity results showed significant differences between groups (chronic condition; VAS ≤ 80) for both instruments at the 1% level. Effect size was moderate for EQ-5D-5L (Cohen's D=0.74; 0.72) and small to moderate for ASCOT (Cohen's D=0.44; 0.69). Test-retest reliability assessment (n=444) revealed moderate to substantial agreement for EQ-5D-5L (k=0.51; 0.68) and fair to moderate agreement for ASCOT (k=0.31; 0.53).

CONCLUSIONS: Psychometric comparison of EQ-5D-5L and ASCOT highlighted distinct constructs, emphasizing complementarity of information the two instruments capture. The study underscores the value of integrating both instruments to broaden the measurement of QoL.