Discounting of delayed rewards across the life span: age differences in individual discounting functions

The present effort addressed both the issue of the generality of choice mod els and the issue of possible qualitative developmental change in temporal discounting by examining behavior at the individual level across the life s pan. Data from individual children, young adults, and older adults who part icipated in two previous studies were analyzed [Green, L., Fry, A.F., Myers on, J., 1994. Discounting of delayed rewards: a life-span comparison. Psych ol. Sci. 5, 33-36; Green, L., Myerson, J., Lichtman, D., Rosen, S., Fry, A. , 1996. Temporal discounting in choice between delayed rewards: the role of age and income. Psychol. Aging 11, 79-84]. At all ages, a hyperbola-like f unction originally proposed by Green et al. (1994) based on group data, pro vided the best description of individual discounting functions. Two develop mental trends were observed. The rate at which individuals discounted the v alue of delayed rewards decreased with age, and there was a systematic chan ge in the shape of the discounting function. Each of these trends was refle cted in a separate parameter of the model. The fact that the same mathemati cal model described the behavior of individuals of different ages suggests that age and individual differences in the discounting of delayed rewards a re primarily quantitative in nature and reflect variations on fundamentally similar choice processes. (C) 1999 Elsevier Science B.V. All rights reserv ed.