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Delay, probability, and social discounting in a public goods game - PubMed

Delay, probability, and social discounting in a public goods game

Bryan A Jones et al. J Exp Anal Behav. 2009 Jan.

Abstract

A human social discount function measures the value to a person of a reward to another person at a given social distance. Just as delay discounting is a hyperbolic function of delay, and probability discounting is a hyperbolic function of odds-against, social discounting is a hyperbolic function of social distance. Experiment 1 obtained individual social, delay, and probability discount functions for a hypothetical $75 reward; participants also indicated how much of an initial $100 endowment they would contribute to a common investment in a public good. Steepness of discounting correlated, across participants, among all three discount dimensions. However, only social and probability discounting were correlated with the public-good contribution; high public-good contributors were more altruistic and also less risk averse than low contributors. Experiment 2 obtained social discount functions with hypothetical $75 rewards and delay discount functions with hypothetical $1,000 rewards, as well as public-good contributions. The results replicated those of Experiment 1; steepness of the two forms of discounting correlated with each other across participants but only social discounting correlated with the public-good contribution. Most participants in Experiment 2 predicted that the average contribution would be lower than their own contribution.

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Figures

Fig 1
Fig 1

Upper graph: Social discount function: Amount of money for the participant equivalent to $75 for a person at a given social distance (N). The solid circles are median crossover points. The line is Equation 1 fit to the medians. Open squares are crossover points of the participant at the 80th percentile (k  =  .04); open triangles are crossover points of the participant at the 20th percentile (k  =  .27). Middle graph: Delay discount function: Amount of money now equivalent to $75 delayed by D days. The solid circles are median crossover points. The line is Equation 2 fit to the medians. Open squares are crossover points of the participant at the 80th percentile (k  =  .01); open triangles are crossover points of the participant at the 20th percentile (k  =  .09). Lower graph: Probability discount function: Amount of money for sure equivalent to $75 at a given odds against (θ  =  (1−p)/p). The solid circles are median crossover points. The line is Equation 3 fit to the medians. Open squares are crossover points of the participant at the 80th percentile (k  =  2.8); open triangles are crossover points of the participant at the 20th percentile (k  =  9.0).

Fig 2
Fig 2

Upper graph: Social AUC versus delay AUC of individual participants. Lower graph: Social AUC versus probability AUC of individual participants. The different numbers of points in the two graphs at the same abscissa value are due to elimination from analysis of delay or probability data of participants who crossed over more than once on that measure. The solid lines are regression lines. The dotted lines are medians.

Fig 3
Fig 3

Distributions of stated PGG contributions in Experiment 1 and Experiment 2 and predictions of average contribution in Experiment 2.

Fig 4
Fig 4

The actual contribution versus predicted contribution in Experiment 2. The solid line is the best linear fit between contribution and prediction.

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