Delayed Reward Discounting and Addictive Behavior: A Meta-Analysis and Review of the Evidence for Causative and Consequential Roles
James MacKillop, University of Georgia
Dr. James MacKillop received his Ph.D. in clinical psychology from the State University of New York at Binghamton and was a clinical intern and postdoctoral fellow at the Center for Alcohol and Addiction Studies at Brown University. He is currently an assistant professor in the Psychology Department at the University of Georgia and an adjunct assistant professor at the Center for Alcohol and Addiction Studies. Dr. MacKillop uses behavioral economics as a framework for understanding addictive behavior in general and applies the approach to alcoholism, nicotine dependence, and pathological gambling in particular. Specific foci include investigating the roles of impulsive delay discounting and excessive drug demand in addictive behavior on multiple levels of analysis. His research applies a translational approach, seeking to apply insights from behavioral, neurobiological, and genetic research to clinical interventions and other applied contexts. He has published more than 60 journal articles, book chapters, and other works in this area and his research is funded by the National Institute on Alcohol Abuse and Alcoholism, the National Institute on Drug Abuse, the Robert Wood Johnson Foundation, and the Alcoholic Beverage Medical Research Foundation, among others.
Abstract: Delayed reward discounting (DRD) is a behavioral economic index of impulsivity. Numerous studies reported more impulsive DRD in groups exhibiting addictive behavior compared to control groups. This presentation will synthesize findings across the literature using a meta-analysis of these studies. Specifically, the meta-analysis will characterize: (a) overall patterns of findings, qualitatively and quantitatively; (b) systematic variability by sample and study type; and, (c) possible small study (publication) bias. Literature reviews identified 310 candidate articles from which 47 studies reporting 67 comparisons were identified (total N = 56,013). From the total comparisons identified, a highly statistically significant but small magnitude effect was evident with extremely high heterogeneity of effect size. Based on systematic observed differences, large studies assessing DRD with a small number of self-report items were removed and an analysis of 60 comparisons (n = 3,329) using equivalent methods and exhibiting acceptable heterogeneity revealed a highly significant medium magnitude effect. Further analyses revealed significantly larger effect sizes for studies using clinical samples (d = .62) compared to studies using nonclinical samples (d = .44). Indices of small study bias among the various comparisons suggested varying levels of influence by unpublished findings, ranging from minimal to moderate. These results reveal consistent evidence of more impulsive DRD in individuals exhibiting addictive behavior that is of medium effect size in general and significantly larger in individuals who meet criteria for an addictive disorder. Moreover, these findings suggest that multi-item assessments of DRD that offer more precise estimates of discounting are more sensitive to group differences. However, the studies reviewed use cross-sectional designs that do not permit a clear inference of whether these differences are causative (etiological) or consequential (symptomatic) of addictive behavior. To address this, several lines of research will be reviewed, including: (a) longitudinal evidence of DRD predicting addictive behavior; (b) evidence of the temporal stability of DRD; (c) evidence of DRD predicting clinical outcomes; (d) evidence from animal studies bearing on etiology; and (e) evidence of genetic influences on DRD and related phenotypes. On balance, most of the studies in these areas suggest that DRD plays an etiological role but there is also evidence that DRD is further exacerbated by drug abuse and aspects of addiction, such as withdrawal and craving. A potentially interactive and recursive process will be discussed.