Probability discounting and gambling: a meta-analysis

A number of studies have investigated connections between probability discounting and gambling. The aim of this research was to obtain a meta-analytical weighted effect size for the relationship between shallow probability discounting (the tendency to overvalue reinforcement with lower odds) and gambling intensity and to examine whether a gambling diagnosis moderated this effect size such that the relationship is stronger for diagnosed problem gamblers.

A database search identified studies that (a) measured both probability discounting and gambling and (b) reported statistical results allowing calculation of an effect size for meta-analysis. The search resulted in 12 studies reporting statistical results for probability discounting and gambling. The studies comprised 1685 individuals from different cohorts and nations, and included gamblers and non-gamblers. The studies reported 18 effect sizes. Across studies, gambling severity was assessed through diagnosis and gambling intensity was assessed through self-report and performance. Comprehensive Meta Analysis software calculated the weighted effect size and moderating role of gambling diagnosis.

Shallower probability discounting was associated with greater gambling severity or intensity in all 12 studies. Throughout the studies, the weighted meta-analytical effect size for the connection between probability discounting and gambling was significant, with Hedges' g = 0.36 [standard error (SE) = 0.07, 95% confidence interval (CI) = 0.21, 0.50), P < 0.001]. Addressing the second aim of the study, individuals diagnosed with a gambling disorder or problem gambling compared with not diagnosed individuals showed an effect size of Hedges' g = 0.79 (SE = 0.18, 95% CI = 0.45, 1.14) and a moderation analysis indicated that this type of comparison showed significantly stronger effects than effect sizes based on associations between probability discounting and gambling (Q₍₁₎ = 7.80, P = 0.005).

There appears to be a positive association between problem gambling and shallow probability discounting (a cognitive bias that overvalues low probability gains and/or undervalues high probability losses).