Attention-Deficit/Hyperactivity Disorder and Monetary Delay Discounting: A Meta-Analysis of Case-Control Studies

ABSTRACTBackgroundA growing number of studies have investigated delay discounting, a behavioral economic index of impulsivity, and its relevance to attention-deficit/hyperactivity disorder (ADHD), but with mixed findings. The current meta-analysis synthesizes the literature on the relationship between monetary delay discounting and ADHD in studies using case-control designs. Specifically, the objectives were as follows: 1) to characterize the aggregated differences in monetary delay discounting between individuals with ADHD (cases) and control subjects in studies using categorical case-control designs; 2) to examine potential differences based on sample age (<18 vs. >18), reward outcome (real vs. hypothetical), and prevalence of conduct disorder and oppositional defiant disorder in the sample; and 3) to evaluate potential small-study (publication) bias in the literature.MethodsFrom 567 candidate articles, 21 independent investigations yielded 25 case-control comparisons (total N = 3913). Random effects meta-analysis was conducted using Cohen's d as the common effect size. Publication bias was evaluated using fail-safe N, Begg-Mazumdar and Egger tests, and meta-regression of publication year and effect size.ResultsAcross studies, a statistically significant difference of medium magnitude effect size was present for the case-control comparisons (d = .43; p < 10−15). No significant differences based on sample age, reward outcome, or comorbid status were detected. Minimal heterogeneity and evidence of publication bias were present.ConclusionsThese findings provide robust evidence that delay discounting is significantly elevated among individuals with ADHD compared with control subjects. Gaps in the literature and the importance of characterizing the neural and genetic bases of this relationship are discussed.