Willingness to Pay per QALY: A Systematic Review of Demand-Side Valuations with a Focus on Age and Disease Severity.

Background: Willingness-to-pay (WTP) studies offer a demand-side perspective on the monetary value of health gains, typically expressed as WTP per quality-adjusted life year (WTP/Q). These estimates can complement supply-side cost-effectiveness thresholds (CETs) and inform whether healthcare budgets align with public preferences. However, existing thresholds often overlook heterogeneity by condition or population characteristics.

Objective: This study sought to systematically review literature on WTP/Q estimates derived from stated preference methods by (i) mapping the broader landscape of demand-side valuations and (ii) synthesizing how WTP/Q varies by both respondent and scenario-assigned age and disease severity in general-health contexts.

Methods: A systematic review was conducted across Medline, Embase, and EconLit, following Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Eligible studies estimated the monetary value of a quality-adjusted life year (QALY) from a societal, demand-side perspective. We first conducted a broad narrative mapping of all included studies to describe methodological characteristics and contextual diversity. We then focused on a subset of studies using general-health scenarios to explore how willingness to pay per QALY varied by age and severity. A structured four-axis framework was applied to distinguish between respondent characteristics and scenario-assigned attributes. Data were classified and tabulated. A formal quality assessment was conducted across the full set of studies using the National Institutes of Health (NIH) tool.

Results: A total of 67 studies met inclusion criteria. Most originated from high-income countries and used contingent valuation or discrete choice experiments. Among general-health studies, WTP/Q decreased with respondents' actual age in 49% of studies and increased with respondents' own health severity in 79%. In studies assessing scenario-assigned attributes, WTP/Q increased with hypothetical disease severity in 91% of studies and decreased with scenario-assigned age in 83%. Substantial heterogeneity was observed in elicitation methods, framing, and utility measurement.

Conclusions: The findings support the need for condition- and population-specific WTP thresholds, as valuations appear to vary depending on the nature of the health gain and the characteristics of the beneficiary-whether real or hypothetical.