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Document Type

Feature Article

Publication Date

Spring 5-1-2009

Publication Title

Washington University Undergraduate Research Digest: WUURD 4(2)


Peer Editor: Sarah Frazier; Faculty Mentor: Leonard Green

Individuals discount the value of delayed and probabilistic rewards according to the same hyperboloid function: V=A/(1+bX)s, where V is the present, subjective value of a reward of amount A, X is the time until it is received (delay) or the odds against it being received (probability), b is a parameter that determines the rate at which the subjective value decreases, and s represents the non-linear scaling of amount and/or time or probability. With delayed rewards, as amount increases, the value of the rate parameter (b) decreases but the exponent (s) remains constant. The goal of the current study was to determine how increases in amount of the probabilistic reward influence these parameters. Subjects discounted nine probabilistic amounts ranging from $20 to $10 million. In contrast to the discounting of delayed rewards, as amount of probabilistic reward increased, s increased but amount had little systematic effect on the value of b. Thus, although the same mathematical function describes both delay and probability discounting, the differential effects of amount argue that the processes underlying probability and delay discounting are different.

From the Washington University Undergraduate Research Digest: WUURD, Volume 4, Issue 2, Spring 2009. Published by the Office of Undergraduate Research.

Henry Biggs, Director of Undergraduate Research and Associate Dean in the College of Arts & Sciences; Joy Zalis Kiefer, Undergraduate Research Coordinator, Co-editor, and Assistant Dean in the College of Arts & Sciences; Kristin Sobotka, Editor.


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