Modifying the quality-adjusted life year calculation to account for meaningful change in health-related quality of life: insights from a pragmatic clinical trial

Abstract

Background: We propose a modified quality-adjusted life year (QALY) calculation that aims to be consistent with guidance for interpreting change in patient-reported outcomes. This calculation incorporates the minimally important difference (MID) in generic preference-based health-related quality of life (HRQL) change scores to reflect what might be considered meaningful HRQL improvement/deterioration. In doing so, we review common issues in QALY calculations such as adjustment for baseline scores and standardizing for between-group differences.

Methods: Using EQ-5D-5L outcome data from the Alberta TEAMCare-Primary Care Network trial in the management of depression for patients with type 2 diabetes (n = 98), this study compared results from different QALY calculation methods to investigate the impact of (i) adjusting for baseline HRQL score, (ii) standardizing between-group differences at baseline, and (iii) adjusting for 'meaningful' HRQL changes. The following QALY calculation methods are examined: area under curve (QALY-AUC), change from baseline (QALY-CFB), regression modelling (QALY-R), and incorporating an MID for HRQL changes from baseline (QALY-MID).

Results: The incremental QALY-AUC estimate favoured the Collaborative Care group (0.031) while the incremental QALY-CFB (-0.028) estimate favoured Enhanced Care. Adjusting for meaningful HRQL changes resulted in a crude incremental QALY-MID of -0.023; however, after adjusting for between-group differences at baseline, QALY-R and adjusted incremental QALY-MID estimates were -0.007 and -0.001, respectively. In addition, recursive regression analyses showed that very low baseline HRQL scores impact incremental QALY estimates.

Conclusions: Uncertainty in incremental QALY estimates reflects uncertainty in the value of small within-individual change as well as the impact of small differences between groups at baseline. Applying a responder-definition approach yielded crude and adjusted QALY-MID estimates that were more in favour of Collaborative Care than QALY-CFB and QALY-R estimates, respectively, suggesting that ambiguous small changes in HRQL scores have the potential to influence QALY outcomes used in economic or non-economic applications.

Keywords: Depression; Health-related quality of life; Minimally important difference; Quality-adjusted life year; Type 2 diabetes.