Valuing prevention through economic evaluation: some considerations regarding the choice of discount model for health effects with focus on infectious diseases.

In cost-effectiveness analysis, the valuing of costs and health effects over time remains a controversial issue. The debate mostly focuses on whether the discount rates for health and money should be equal and which discounting model and time preferences are most appropriate. In this paper we add to the debate by arguing that the assessment of effectiveness of a preventive intervention may influence the choice of the discounting procedure for health. Health effects in cost-effectiveness analysis are commonly expressed in life-years gained, QALYs gained or lives saved. These denominators are only indirect and partial measures of the effects of a preventive intervention. The actual effect of the intervention is a reduction of the risk of mortality and morbidity in a given period of time. This risk reduction will not always coincide with the moment at which the impact on (quality-adjusted) life-years gained is made (i.e. at risk exposure), for example when preventing chronic disease with an asymptomatic stage. In this paper we show that truly acknowledging the origin of health benefits could have implications for the discounting procedure. We present a discounting model that adequately focuses on the reduction of risk. This model recognises the potential interpretation of risk reduction for infection as an economic good to be acquired with associated mortality reductions as later indirect effects. This implies that our suggested discounting model focuses on the moment(s) of risk reduction. A numerical example illustrates our approach. We discuss the associated potential implications for public health policy and discuss how the effects of the intervention can be additionally corrected for societal preferences.