Societal discounting of health effects in cost-effectiveness analyses: the influence of life expectancy.

Background: Increasing life expectancy and decreasing marginal valuation of additional QALYs over time may serve as a basis for discounting future health effects from a societal perspective. Therefore, we tested the hypothesis that societal time preference for health is related to perceived future life expectancy.

Methods: A sample of 223 people from the general population prioritised healthcare programmes with differential timing of health benefits and costs from a societal perspective. Furthermore, we asked respondents to estimate future life expectancy.

Results: The relationship between future life expectancy and time preference for health is ambiguous. We observed that people who expected a higher future life expectancy elicited higher discount rates for health effects than those with lower life expectancy growth expectations for all four time periods (5, 10, 20 and 40 years into the future), but the differences were never significant. On average, providing explicit information on growth in life expectancy did significantly alter discount rates in the expected direction but, on an individual level, the results were rather inconsistent. We observed a significantly stronger time preference (i.e. higher discount rates) for health effects than for costs. As commonly observed, discount rates for health and money decreased with time delay following a hyperbolic function.

Conclusion: Our data indicate that it is troublesome to elicit societal discount rates empirically, especially rates that are in line with the theoretical arguments on societal discounting. The influence of life expectancy remains ambiguous, but there seems to be at least some positive relationship between growth in life expectancy and discount rates that deserves additional attention.