This study examines the effectiveness of using vouchers to reinforce either the provision of urine samples testing negative for illicit drugs (UA group) or the completion of objective, individually defined, treatment-plan-related tasks (TP group). A third group was assigned to the clinic's standard treatment (STD group). Participants were randomly assigned to groups after a 6-week baseline-stabilization period. Urine specimens were collected thrice weekly throughout the study. In the UA condition, participants earned $5 (U.S. dollars) in vouchers for each drug-free urine submitted. In the TP condition, participants earned up to $15 in vouchers per week for demonstrating completion of treatment plan tasks assigned by their counselors. Contingencies were in effect for 12 weeks, after which all participants received the clinic's standard treatment. Urinalysis results indicate that the TP intervention was significantly more effective in reducing illicit drug use than either the UA or STD interventions. These effects were maintained with a trend toward continuing improvement for the TP groups even after contingencies were discontinued.

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This study examines an approach to identifying patterns of treatment response over time. Treatment response profiles are identified by cluster analyzing a repeated measure of patient performance collected at intervals during treatment. The procedure is demonstrated in Study 1 using monthly urinalysis results of 103 patients entering methadone maintenance treatment. The internal, external, and face validities of derived treatment response profiles are evaluated. A logistic regression model predicting treatment response is then constructed from intake variables found to correspond with the treatment response profiles. Study 2 replicates the procedures on an independent sample. Treatment response profiles facilitate the analysis of treatment response offering advantages over common measures of treatment outcome, such as performance at follow-up, change in performance from treatment entry to follow-up, or performance summed across treatment.

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This study compared 2 alternate measures of stage of change as conceived by J. O. Prochaska and C. C. DiClemente. A sample of 276 methadone maintenance patients completed both categorical and dimensional measures of stage of change regarding quitting illicit drug use. The categorical measure places participants into 1 of 5 stages based on their stated intentions regarding future illicit drug use. The University of Rhode Island Change Assessment scale (URICA) provides continuous scores on 4 stage-of-change scales. Confirmatory factor analysis was used to assess the URICA's factor structure. The relationship between URICA scores and self-reported drug use was also assessed. Comparison of the URICA and the categorical measure using discriminant function analysis indicated limited convergence between the 2 measures and suggests that they may assess different aspects of readiness to change.The stages-of-change model developed by Prochaska, DiClemente, and colleagues has gained increasing popularity as a way of conceptualizing readiness to change. The model posits that behavior change occurs in a developmental progression characterized by five distinct stages: precontemplation, contemplation, preparation, action, and maintenance. In their efforts to effect change, individuals at different stages are believed to make use of distinct constellations of activities or processes of change. Measures derived from this model have been used to assess stages and processes of change with respect to a wide variety of behaviors, including smoking cessation (Di-