Modelling Informal Carers' Health-Related Quality of Life: Challenges for Economic Evaluation.

There has been increasing interest in including carers' health-related qualify of life (HRQoL) in decision models, but currently there is no best practice guidance as to how to do so. Models thus far have typically assumed that carers' HRQoL can be predicted from patient health states, as we illustrate with three examples of disease-modifying treatments. However, this approach limits the mechanisms that influence carers' HRQoL solely to patient health and may not accurately reflect carers' outcomes. In this article, we identify and discuss challenges associated with modelling intervention effects on carers' HRQoL: attaching carer utilities to patient disease states, the size of the caring network, aggregation of carer and patient HRQoL, patient death, and modelling longer-term carer HRQoL. We review and critique potential alternatives to modelling carers' HRQoL in decision models: trial-based analyses, qualitative consideration, cost-consequence analysis, and multicriteria decision analysis, noting that each of these also has its own challenges. We provide a framework of issues to consider when modelling carers' HRQoL and suggest how these can be addressed in current practice and future research.