ON BIRDS AND PROMISES: SUBJECTIVE CHOICES

Abstract

One hundred and forty six students enrolled in undergraduate psychology courses at the University of Brasilia in 1992 indicated their preference between a hypothetical fixed amount of money available with various probabilities or delays and a certain reward of variable amount available immediately. In Experiments 1 and 2 amounts of money were stated in Cruzeiros (Cr$) and in Experiments 3 and 4 in US dollars (US$). The function relating the amount of certain-immediate reward subjectively equivalent to the delayed amount had the same general shape (hyperbolic) both when the currency was Cruzeiros or Dollars although the function for  Cruzeiros was steeper. For the same delay, the discounted value for Cruzeiros was relatively higher than for Dollars, possibly reflecting differences in American and Brazilian students’ delay discounting due to differences in confidence in the currency used. A power function related the certain-immediate amount of money subjectively equivalent to the fixed probabilistic reward and was similar for Cruzeiros and Dollars. In Experiment 2 participants chose between a delayed Cr$100.000 reward and a probabilistic Cr$100.000. The choice in Experiment 4 was between a delayed US$1.000 reward and a probabilistic US$1.000 reward. In both experiments delay was proportional to the same odds-against transformation of the probability to which it was subjectively equivalent. The popular sayings “A bird in the hand is worth two in the bush” (probability) and “Promises don’t pay debts” (delay) seem to be supported by the present results. Choices between probable and certain amounts showed the usual pattern previously found, independently of context (e.g., inflation). Promises often specify delayed reinforcer consequences and to trust on promise payer is behavior dependent on previous history of reinforcement.Key words: probability, risk, delay, subjective equivalence, decision, choice.