A Meta-Analysis of Nonsystematic Responding in Delay and Probability Reward Discounting

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Delay discounting (DD) and probability discounting (PD) are behavioral measures of choice that index sensitivity to delayed and probabilistic outcomes, which are associated with a range of negative health-related outcomes. Patterns of discounting tend to be predictable, where preferences for immediate (vs. delayed) and certain (vs. probabilistic) rewards change as a function of delay and probability. However, some participants yield nonsystematic response patterns (NSR) that cannot be accounted for by theories of choice and could have implications for the validity of discounting-related experiments. Johnson and Bickel (2008) outline an algorithm for identifying NSR patterns in discounting, but the typical frequency of and methodological predictors of NSR patterns are not yet established in the extant literature. In this meta-analytic review, we identified papers for analysis by searching Web of Science, PubMed, and PsycInfo databases until November 8, 2015 for experiments identifying nonsystematic responders using Johnson and Bickel’s algorithm. This yielded 114 experiments with nonsystematic data reported. The overall frequency of NSR across DD and PD studies was 18% and 19%, respectively. Nonmonetary outcomes (e.g., drugs, food, sex) yielded significantly more NSR patterns than did discounting for monetary outcomes. Participants recruited from a university setting had significantly more NSR patterns than did participants recruited from nonuniversity settings. Our review also indicates that researchers are inconsistent in whether or how they report NSR in discounting studies, which is relevant for a clearer understanding of the behavioral mechanisms that underlie impulsive choice. We make several recommendations regarding the assessment of NSR in discounting research.

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