Understanding the impact of different approaches to combine carer and patient utilities in decision-analytic model-based cost-effectiveness analysis

Abstract

Abstract Background: The National Institute for Health and Care Excellence’s (NICE’s) reference case states that all direct health effects for patients or carers should be included in economic evaluations. However, no recommended method has been published to incorporate carer health-related quality of life (HRQoL) in economic models. Thus, the additive, multiplicative, minimum and adjusted decrement estimator (ADE) approaches that are usually used to combine multiple utilities for a patient in the case of comorbidities have been used to combine patient and carer utilities in the current study. Objectives: To understand the impact of using different approaches to incorporate patient and carer utilities on the results of a cost-effectiveness model. Literature review: A systematic literature review was undertaken to update Pennington et al.’s previous systematic review of the inclusion of carer HRQoL in the NICE appraisals. All recent Technology Appraisals (TAs) and Highly Specialised Technologies (HSTs) were reviewed, and it was found that 6 of the 176 TAs and all 7 HSTs included carer HRQoL in their economic analyses. Methods: A state transition model of nusinersen early-onset SMA against best supportive care (BSC) was developed. The model starting point is to use carer disutilities. Then, four different approaches were applied in the model to explore the impact of combining patient and carer utilities on quality-adjusted life years (QALYs) and the incremental cost-effectiveness ratio (ICER). Results: The incremental QALYs obtained using the carer disutilities approach in the SMA Type 1 model was 0.56 with an ICER of £4,975,231 per patient QALY gained. After applying the different approaches, the incremental QALYs resulting from the additive approach was 39.99 with an ICER of £69,505 per QALY gained while the multiplicative approach was 14.66 with an ICER of £189,547 per QALY gained, and the minimum and ADE approaches were 31.44 and 31.01 with an ICER of £88,396 and £89,635 per QALY gained, respectively. Conclusion: The impact of using different approaches is an increase in the incremental QALYs and a reduction in ICERs compared to the usual approach of estimating carer disutilities. The additive approach has the greatest impact while the multiplicative approach has the lowest impact on QALYs and ICER compared to other approaches.