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Objectives: We applied principles for conducting economic evaluations of factorial trials to a trial-based economic evaluation of a cluster-randomised 2x2x2 factorial trial. We assessed the cost-effectiveness of atorvastatin, omega-3 fish oil and an action-planning leaflet, alone and in combination, from a UK NHS perspective. Methods: The Atorvastatin in Factorial with Omega EE90 Risk Reduction in Diabetes (AFORRD) trial randomised 800 patients with type 2 diabetes to atorvastatin, omega-3 or their respective placebos and randomised general practices to receive a leaflet-based action-planning intervention designed to improve compliance, or standard care. Sixteen-week outcomes for each trial participant were extrapolated for 70 years using the United Kingdom Prospective Diabetes Study Outcomes Model v2.01 (UKPDS-OM2). We analysed the trial as a 2x2 factorial trial (ignoring interactions between action-planning leaflet and medication), as a 2x2x2 factorial trial (considering all interactions), and ignoring all interactions. Results: We observed several qualitative interactions for costs and quality-adjusted life-years (QALYs) that changed treatment rankings. However, different approaches to analysing the factorial design did not change the conclusions. There was ≥99% chance that atorvastatin is cost-effective and omega-3 is not at a £20,000/QALY threshold. Conclusions: Atorvastatin monotherapy was the most cost-effective combination of the three trial interventions at a £20,000/QALY threshold. Omega-3 fish oil was not cost-effective, while there was insufficient evidence to draw firm conclusions about action-planning. Recently-developed methods for analysing factorial trials and combining parameter and sampling uncertainty were extended to estimate cost-effectiveness acceptability curves within a 2x2x2 factorial design with model-based extrapolation. Trial registration: ISRCT 76737502

Type

Journal

Value in Health

Publisher

Elsevier

Publication Date

21/05/2020

Keywords

economic evaluation, type 2 diabetes, randomised controlled trial, individual patient simulation model, factorial design, lipids, adherence