Da. Redelmeier et Dn. Heller, TIME PREFERENCE IN MEDICAL DECISION-MAKING AND COST-EFFECTIVENESS ANALYSIS, Medical decision making, 13(3), 1993, pp. 212-217
Cost-effectiveness analyses usually quantify peoples' attitudes toward
s delayed outcomes using the exponential discount model. The authors e
xamined three assumptions of this model by assessing the time preferen
ces of individuals towards hypothetical health states and calculating
implicit annual discount rates. Of a random sample of medical students
, house officers, and attending physicians, 121 participated, reflecti
ng a response rate of 81%. The participants considered three temporary
events (colostomy, blindness, depression) that were destined to occur
at five sequentially distant times in the future (one day, six months
, one year, five years, and ten years). The utility of each prospect w
as measured using two elicitation techniques (standard gamble and cate
gorical scaling), and 1,394 implicit discount rates were calculated. O
f all the discount rates, 62.1% equalled zero, 10.0% were less than 0.
00, and 15.7% were greater than 0.10. Mean discount rates for relative
ly proximal time intervals tended to be larger than those for relative
ly more distant intervals (0.041 vs. 0.025, p < 0.01). Mean discount r
ates for blindness tended to be smaller than those for colostomy or de
pression (0.023 vs 0.039 vs 0.037, respectively, p < 0.005). Hence, pe
oples' implicit discount rates are not always small positive numbers t
hat are constant over time and the same for all settings. The authors
suggest that the conventional exponential discount model may not fully
characterize the time preferences held by individuals.