Petry, Alessi, and Hanson (2007) combined data from three randomized clinical trials of contingency management to determine whether the quality of life of cocaine abusers who received contingency management (CM) differed significantly from patients who received standard care. The study included 393 individuals who participated in one of three CM studies from 1999 to 2003 (Petry et al. 2006; Petry et al. 2005; Petry et al. 2004). The three studies occurred at four drug abuse treatment clinics in Connecticut and Massachusetts. Recruitment for the studies occurred between September 1998 and January 2004, and follow-ups of study participants occurred between October 1998 and September 2004.
Substance users were eligible to participate in the study if they were initiating intensive outpatient treatment at one of the four clinics and met the Diagnostic and Statistical Manual of Mental Disorders (DSM–IV) criteria for cocaine abuse or dependence. Substance abusers were ineligible to participate if they were unable to comprehend the study, had an active psychotic disorder, were currently suicidal, or were in recovery for pathological gambling.
There were 278 patients randomly assigned to receive CM and 115 patients randomly assigned to receive standard treatment across the three studies. The CM treatment group was 48 percent male, and 53.0 percent African American, 33.5 percent European American, 11.2 percent Hispanic/Latino, and 2.5 percent other. Age averaged 36.1 years. The standard care control group was 54.8 percent male and 51.3 percent African American, 37.4 percent European American, 11.3 percent Hispanic/Latino, with an average age of 36.4 years. There were no significant differences between the groups.
Study participants completed a 2-hour interview that captured demographic information and assessed drug use diagnoses and pathological gambling based on the Structured Clinical Interview from DSM–IV. Breath and urine samples were also collected and screened for alcohol, cocaine, and opioid use. The Quality of Life Inventory (QOLI) assessed the importance and satisfaction in 17 life areas. The total scale score is obtained by averaging all subscale scores for each domain that is rated as important or extremely important by participants. The QOLI total score reflects subjective well-being in life domains considered of some importance to participants. The QOLI was administered again at 1, 3, 6, and 9 months after treatment began.
The standard treatment condition included group therapy sessions that involved relapse prevention, coping and life skills training, AIDS education, and 12-step treatment. Intensive case (up to 5 hours a day, 5 days a week) lasted 2 to 4 weeks. Aftercare consisted of one group session a week for up to 12 months. Study participants who received standard care submitted breath and urine samples 3 days a week in weeks 1 to 3, 2 days a week in weeks 4 to 6, and once a week in weeks 7 to 12 of the studies.
CM treatment consisted of the same standard care that the control group received plus the chance to earn prizes or vouchers for submitting negative samples and/or completing goal-related activities. Each of the three studies included in the analysis evaluated two CM procedures that differed by magnitude of prizes available (Petry et al. 2004), type of reinforcement (Petry et al. 2005), or behaviors reinforced (Petry et al. 2006). In two of the studies (Petry et al. 2005; Petry et al. 2004), patients received reinforcements for two behaviors—submission of negative samples and completion of goal-related activities. The number of draws earned started at one draw per one negative sample or activity completed, with bonuses of five draws or a $10 voucher for a full week of negative samples or three activities completed within a week. During the third study (Petry et al. 2004), participants earned draws associated with $1, $20, and $100 prizes, with an expected maximal earning of about $240.
For this study, participants from all three studies were combined into one group, and participants who did not receive CM were combined into the standard treatment group. Hierarchical linear modeling was used to evaluate changes in the QOLI total scores from baseline through month 9. The study also included examination of drug abstinence as a mediated effect of CM on QOLI total scores. The main outcome measure in each study was longest duration of abstinence (LDA) achieved during treatment. LDA was defined as consecutive weeks in which all samples tested negative for opioids, cocaine, and alcohol, ranging from 0 to 12 weeks.
There were four steps of mediation analyses also conducted. Step 1 evaluated whether CM engendered significant improvements relative to standard treatment on QOLI scores over time. Step 2 examined whether CM significantly improved durations of abstinence. Step 3 evaluated partial corrections between LDA and posttreatment QOLI scores. Step 4 assessed whether inclusion of LDA as a between-participants predictor rendered the relationship found in step 1 nonsignificant.
Petry and colleagues (2005) evaluated the efficacy of prize-based incentives contingency management intervention as an addition to usual care in community treatment settings. The study included 415 cocaine or methamphetamine users from eight outpatient community clinics located in urban, suburban, and rural settings through the country.
Patients at the clinics were enrolled between April 30, 2001, and Feb. 28, 2003. Patients were eligible to participate if: they reported stimulant use within 2 weeks of study entry; exited a controlled environment (detoxification unit, hospital, or correctional facility) within 2 weeks of study entry and reported stimulant use within 2 weeks of entering the controlled environment; or submitted a stimulant-positive urine sample as treatment entry without self-reporting stimulant use. Eligible participants completed a 90-minute interview before random assignment. Information was gathered on demographics, psychosocial problems, and lifetime and current drug use, including DSM–IV substance use diagnoses. Participants also provided first-study urine samples. Participants were then randomly assigned to either usual care or usual care plus abstinence-based incentives for 12 weeks.
The usual care condition consisted primarily of group counseling, and possibly individual and family counseling as well. Participants received immediate feedback on urinalysis results, and staff congratulated participants if they tested negative. The abstinence incentives group earned the chance to win prizes when their test results were negative for cocaine, amphetamine, methamphetamine, and alcohol (primary target drug). Participants with negative tests were allowed to draw 1 to 12 chips from a container that had 500 chips. The number of chips a participant was permitted to draw was determined on a schedule that was responsive to test outcomes. Draws increased by one each week in which all submitted samples were free of the primary target drugs. Each chip had a different reward value, ranging from Good Job (worth no reward), to Small (worth $1 in prizes), to Large (worth $20 in prizes), to Jumbo (worth $80 to $100 in prizes).
The usual care group was 44.7 percent male, and 40.3 percent African American, 39.3 percent White, 12.1 percent Hispanic, and 8.3 percent other, with an average age of 35.7 years. The incentives group was 44.5 percent male, and 31.6 percent African American, 45.0 percent White, 12.9 percent Hispanic, 10.5 percent other, with an average age of 35.9 years. There were no significant differences between the groups, except on marital status (the incentives group had a higher percentage of participants who had never been married and a lower percentage who were married or cohabitating).
The outcome measures of interest were retention, study compliance, treatment participation, and substance use. Retention was measured as the number of days that elapsed between the first and last study urine samples that were submitted. Study compliance was the percentage of participants who submitted at least one sample per week during the study. Treatment participation was defined as the number of counseling sessions attended during the 12-week study, including individual, group, and family counseling sessions.
To account for missing or incomplete data, substance use was evaluated in several ways: overall percentage of submitted samples that were free of each target drug (stimulants, alcohol, opioids, and marijuana), percentage of samples submitted that were free of stimulants and alcohol at each of the 24 study visits, total number of stimulant- and alcohol-free samples submitted by each participant, and longest duration of abstinence from the primary target drug for each participant.
The study used t–tests for continued variables and chi-square tests for dichotomous variables when examining between-group differences on baseline measures. Study retention was examined using the Cox proportional hazards model. Binary variables that repeated across time were analyzed using generalized estimating equations. Results from this analysis were reported as odds ratios. Individual differences in outcomes were measured using t–tests, Mann–Whitney tests, and chi-square tests.