Time discounting and quality of life are two important factors in evaluations of medical interventions. The measurement of these two factors is complicated because they interact. Existing methods either simply assume one factor given, based on heuristic assumptions, or invoke complicating extraneous factors, such as risk, that generate extra biases. The authors introduce a method for measuring discounting (and then quality of life) that involves no extraneous factors and that avoids distorting interactions. Their method is considerably simpler and more realistic for subjects than existing methods. It is entirely choice based and thus can be founded on economic rationality requirements. An experiment demonstrates the feasibility of this method and its advantages over classical methods. Key words: utility measurement; discounting; QALY; utility of life duration; time tradeoff (Med Decis Making 2012;32:583-593) Q uality-adjusted life year (QALY) evaluations integrate two components, quality of life and discounting (utility of life duration). These components interact, and it is hard to measure one without knowing the other.1 Most measurements of one component assume the other component known, based on heuristic assumptions. Thus, in time tradeoff (TTO) measurements of quality of life, utility of life duration is usually assumed to be linear (no discounting). In measurements of discounting, outcomes are usually monetary, with the utility of money assumed to be linear. Whether discounting of health can be equated with discounting of money remains a point of debate.
2-5Only few attempts have been made to avoid the interaction between discounting and quality of life, and these invoke extraneous factors such as risky or interpersonal (utilitarian) aggregations.1,6-10 Then attitudes toward risk and welfare intervene and generate additional biases.
11-16This article presents a method to measure discounting within the QALY model that avoids the aforementioned problems: Our method (a) needs no extraneous factors, (b) is not affected by the interactions between discounting and quality of life, and (c) uses stimuli that can be simpler and more realistic than those for existing methods. We can measure any general discount function, constant or not. Because we avoid all extraneous factors and interactions, we call our method the direct method (DM). With utility of life duration (discounting) measured, we can also measure quality of life by correcting traditional TTO measurements. We can thus measure the whole QALY model.Unlike classical methods for measuring the utility of life duration and discounting (the standard gamble method and the certainty equivalence [CE] method), which are based on risky decisions, we need not invoke the outcome of immediate death. This outcome is very aversive and is known to arouse negative and distorting emotions.* Especially problematic for classical measurements is that, besides immediate death, they also need scenarios of sure death at Received 26 February 2011 from iBMG/iMTA (AEA, HB) and the D...