| Abstract: Delay discounting (DD) and Probability Discounting (PD) are behavioral measures of impulsive choice. Discounting patterns tend to be predictable, where immediate (or certain) rewards are valued more than relatively delayed (or uncertain) rewards in a systematic way. However, some participants exhibit nonsystematic response patterns (NSR) that diverge from general expectations, which could have implications for the validity of discounting-related experiments. We meta-analyzed the findings from 114 discounting studies (from 78 total papers) that reported using Johnson and Bickels (2008) algorithms for identifying NSR and examined (1) the frequency of NSR patterns across studies; and (2) potential methodological factors that contribute to increased or decreased frequencies of nonsystematic responding. The overall frequency of NSR across DD and PD studies was 18% and 19%, respectively. Non-monetary outcomes (e.g., drugs, food, sex) yielded more NSR patterns (21%) than did discounting for monetary outcomes (16%; Q(1) = 3.87, p = .049). Our review indicates also 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. |