Background: This study examined the relationships between a newly developed older person-specific non-preference-based quality of life (QoL) instrument (Older People's Quality of Life brief questionnaire (OPQoL-brief)) and two generic preference-based instruments (the EQ-5D-3L Level (EQ-5D-3 L) and the Adult Social Care Outcomes Toolkit (ASCOT) in a community-dwelling population of Australian older people receiving aged care services.
Methods: We formulated hypotheses about the convergent validity between the instruments (examined by Wilcoxon-Mann Whitney, Kruskal Wallis and Spearman's correlation tests) and levels of agreement (assessed using intra class correlation (ICC) and modified Bland-Altman plots based on normalized Z EQ-5D-3 L and ASCOT utilities and OPQoL-Brief summary scores).
Results: The utilities/summary scores for 87 participants (aged 65-93 years) were moderately but positively correlated. Moderate convergent validity was evident for a number of instrument dimensions with the strongest relationship (r = 0.57) between 'enjoy life' (OPQoL-Brief) and 'social contact' (ASCOT). The overall ICC was 0.54 and Bland-Altman scatter plots showed 3-6% of normalized Z-scores were outside the 95% limits of agreement suggesting moderate agreement between all three instruments (agreement highest between the OPQoL-Brief and the ASCOT).
Conclusions: Our results suggest that the OPQoL-Brief, the ASCOT and the EQ-5D_3L are suitable for measuring quality of life outcomes in community-dwelling populations of older people. Given the different constructs underpinning these instruments, we recommend that choice of instrument should be guided by the context in which the instruments are being applied. Currently, the OPQoL-Brief is not suitable for use in cost-utility analyses as it is not preference-based. Given their different perspectives, we recommend that both the ASCOT and the EQ-5D are applied simultaneously to capture broader aspects of quality of life and health status within cost-utility analyses within the aged care sector. Future research directed towards the development of a new single preference-based instrument that incorporates both health status and broader aspects of quality of life within quality adjusted life year calculations for older people would be beneficial.