Functional parameters of delay discounting assessment tasks: order of presentation

Several variants in the methods used to estimate delay discounting (DD) have been associated with within-subject differences in degree of DD. This study compared variants in the order of presentation of reward and delay values during assessment of DD of hypothetical cash. Participants were randomly assigned to one of two groups. For one group, the immediate reward values were presented in Ascending order and for the other, they were presented in Descending order. In addition, all participants completed a DD task with the reward values presented in a Random order. Degree of DD, calculated as area under the curve (AUC), was similar between the Ascending and Descending procedures, and was significantly higher with the Random procedure. Within-subjects AUC were positively correlated. Reaction times within choice trials changed systematically as a function of order of presentation of the immediate rewards, and distance to the indifference point within each delay value. Reaction times appear to parallel the effort involved in making the individual choices. Some procedural variants in the assessment of DD yield differences in behavior during the assessment task that affect the magnitude of the estimated delay discounting. Thus, the absolute magnitude of DD may not be directly comparable between methods.