Delay and probability discounting in pathological gamblers with and without a history of substance use problems

Pathological gambling and substance use disorders are highly comorbid, possibly because they both stem from a similar process-impulsivity. Although much data exist regarding the association between delay discounting and these psychiatric disorders, relatively little research has examined probability discounting and its relationship with either substance use or gambling. The goal of the current study was to compare rates of probability and delay discounting in a large population of pathological gamblers with and without a history of substance use problems. Treatment-seeking pathological gamblers with (n = 117) and without (n = 119) a history of substance use problems completed questionnaires about discounting of hypothetical monetary outcomes and the Eysenck Impulsivity Questionnaire. The delay-discounting questionnaire involved choices between a smaller amount of money delivered immediately versus a larger amount delivered later, and the probability questionnaire was comprised of choices between a smaller certain versus a larger probabilistic monetary outcome. Hyperbolic functions estimated delay and probability discounting rates based on the indifference points obtained through the questionnaires. Results revealed significant effects of substance use problem status on delay but not on probability discounting, with no significant correlation noted between the two discounting processes. Only delay discounting correlated with Eysenck impulsivity scores. These data suggest that delay and probability discounting tap different dimensions, and delay discounting is more closely linked with substance use problem histories in pathological gamblers.