Risky Decision Making in Methamphetamine Users: The Role of Opioid Blockade

In the SexPD task, subjects are asked to choose between having sex with a more appealing partner with a varying chance of having a sexually transmitted infection (STI) or a less appealing partner with no STI.

A hyperbolic decay model was used to calculate h, a free parameter that indexes the rate of probabilistic discounting. Smaller h values indicate a preference for probabilistic (i.e., riskier) outcomes. To normalize the data, the natural log of h values were calculated and reported here.

Monetary delay discounting task consisted of choosing between a larger, delayed and a smaller, immediate reward. A hyperbolic decay model was used to calculate k, a free parameter that indexes the rate of delay discounting. As k values are typically skewed across subjects, the distribution of k was normalized by using a natural log transformation. The normalized values are reported here. If k typically ranges between 0.5 and 10^-5, then the natural log of k will range between -0.69 and -11.5. Larger normalized k values indicate a preference for smaller sooner outcomes (i.e., more impulsive decision-making).

The Barrat Impulsiveness Scale (BIS) is a 30 item questionnaire to measure a persons impulsiveness. Items are answered on a 4-point scale and scored 1-4 then summed across responses. Total scores range from 30-120 with a higher summed score indicating higher impulsivity.

The Risk Assessment Battery (RAB) is a 26 question self-administered assessment focusing on drug use, injection and sexual risk during the past 30 days.

Three composite HIV risk scores (drug, sex, and total score) are calculated. The questions have different numbers of items, and scores for a single question can range from 0 to 7, with higher values reflecting more instances of risk behavior. The drug risk score has a range of 0 to 22 and is calculated from 8 questions that address recent substance use, including frequency, needle sharing, and cleaning of the "works." 9 questions are used to calculate a sex risk score that has a range of 0 to 18, and these questions address the frequency and types of sexual behavior, HIV status of sexual partners, and type of protection that was used (if any). Total score is calculated by adding drug and sex scores and dividing by 40, the maximum score possible, and ranges from 0 to 40 where higher scores indicate greater risk behavior.

Participants were asked "How many days in the past 30 days did you use methamphetamine?". This is a self-report measure.