Comparing delay- and probability-discounting rates in offenders and non-offenders.

Discounting rates for hypothetical monetary outcomes that were delayed or probabilistic were obtained for a sample of incarcerated offenders (N = 62) and a control sample of non-offenders (N = 70). Rates were obtained through a questionnaire in which participants indicated an amount of money available immediately (or received with certainty) that would be equal in value to a delayed (or probabilistic) reward. Four amounts were used ($500, $1,000, $2,000 and $4,000), combined factorially with four delays (1 year, 2 years, 4 years, and 8 years) or probabilities of receipt (10%, 25%, 50%, 90% ), yielding 16 discounting rates for both delayed and probabilistic outcomes. Participants' discounting rates decreased with increases in delay, odds against and amount, with offenders discounting both delayed and probabilistic outcomes at higher rates than non-offenders. It was found that the discounting rates were positively correlated within subjects, with a factor analysis revealing that rates for delayed and probabilistic outcomes loaded on two separate factors. Participants also completed the Michigan Alcohol Screening Test (MAST), the Drug Abuse Screening Test (DAST), the Barratt Impulsivity Scale v. 11 (BIS v.11) and the Momingness Eveningness Questionnaire (MEQ), with the offenders reporting overall higher rates of alcohol and drug use and impulsivity. A regression analysis found that the differences in average discounting rates between offenders and non-offenders remained significant when the correlations between self-reported alcohol and drug use and discounting rates were statistically controlled for. Overall, offenders discounted delayed and probabilistic outcomes at a higher rate than nonoffenders, and reported higher levels of alcohol and drug use