The degree to which real and hypothetical rewards were discounted across delays ranging from 6 hr to 1 year was explored in a within-subjects design. An adjusting-amounts procedure was used to estimate the subjective value of real and hypothetical rewards at each delay. A hyperbolic discounting function provided a significantly better fit to individual participants' preferences than did an exponential function. No significant effect of reward type on degree of hyperbolic discounting or area under the discounting curves was detected. These findings offer some support for the validity of using hypothetical rewards to estimate discounting rates in substance-abusing and other populations, but caution is suggested because this support is gleaned from a failure to detect an effect of reward type.

Prior studies comparing discounting of delayed hypothetical or potentially real rewards have reported no differences, but they used within-subjects designs. This raises the possibility that participants remembered their choices in one condition and repeated them in the other. In Experiment 1, between-subjects comparisons were made with an adjusting-amount procedure. No significant effect of reward type on delay discounting was detected. Experiment 2 increased the proportion of real rewards and made between- and within-subject comparisons. These comparisons also failed to reveal a significant effect of reward type. Although these findings are consistent with prior findings, caution is urged because choices involving hypothetical rewards have yet to be compared with choices involving real rewards (i.e., the consequences of every choice are obtained) in an experiment using forced-choice trials and steady-state methodology.

Single-Case Experimental Designs to Evaluate Novel Technology-Based Health Interventions