Effects of Amount on Probability Discounting: A Replication and Extension

We evaluated two quantitative models that attempt to account for the effects of amount on probability discounting. Sixty-four undergraduate psychology students completed four probability discounting tasks that differed in the amount of the probabilistic outcome ($20, $3,000, $50,000, and $500,000). In an amountindependent hyperboloid model, the exponent (s) systematically increased with reward amount. These systematic changes were not explained by the model. Myerson et al. (2011) reasoned that s increases as a power function of the amount of the probabilistic reward. We found support for the amount-dependent hyperboloid model at the aggregate and individual levels of analysis. The results replicate and extend previous research and suggest that the value function of a probabilistic outcome is weighted by, or depends on, its amount.