Time-related issues with application to health gains and losses.

Time-related aspects of health have attracted increasing interest, and it has become evident that many medical situations concern the exchange of present-day costs for future benefits. Traditional decision analytic paradigms weigh the probability of outcomes and the value of outcomes. Such analyses are incomplete if they do not consider the time of the outcome as well. The concept of diminishing value over time is positive discounting. Time discounting processes and effects have a potentially large impact on clinical decision making. Therefore, characteristics of discounting should be taken into consideration. Discounting processes are variable with individuals and also within different contexts such as gains and losses. No single model can be expected to describe time-related decisions within health. A more diversified use and critical appraisal of these concepts in medicine become more important as we attempt to refine decision models. A summary of valuation factors in medical decision making is presented: (a) long-term decisions are very sensitive to discount rates; (b) discount rates are greater for gains than for losses; (c) discount rates vary by domain, by outcome, by individuals over time, and by level of certainty; (d) individual preferences may reverse themselves over time; (e) the doctor uses expected value; the patient is risk aversive; (f) over a lifetime perspective, a flat or even negative discount rate will result in choices that minimize lifetime disability.