Subjective Probability and Delay

Human subjects indicated their preference between a hypothetical 1, 000 reward available with various probabilities or delays and a certain reward of variable amount available immediately. The function relating the amount of the certain-immediate reward subjectively equivalent to the delayed 1, 000 reward had the same general shape (hyperbolic) as the function found by Mazur (1987) to describe pigeons' delay discounting. The function relating the certain-immediate amount of money subjectively equivalent to the probabilistic 1, 000 reward was also hyperbolic, provided that the stated probability was transformed to odds against winning. In a second experiment, when human subjects chose between a delayed 1, 000 reward and a probabilistic 1, 000 reward, delay was proportional to the same odds-against transformation of the probability to which it was subjectively equivalent.