Results from this study suggest that the prize reinforcement CM procedure is efficacious in reducing cocaine use. The beneficial effects appear to be magnitude-dependent, with the low magnitude condition tested in this study not being particularly efficacious. Patients who initiate treatment with a positive urinalysis result may have better outcomes when they receive CM than when they receive standard treatment without CM. In contrast, CM may not be necessary for patients who initiate treatment with a cocaine-negative urinalysis result. These results will be discussed, along with their implications for the use of CM as an add-on to standard therapy at community-based substance abuse treatment programs.
This study found that the $240 CM condition engendered more beneficial effects than standard treatment on the substance use outcome measures. Whether duration of continuous abstinence or percentages of negative samples submitted were used, CM treatment out-performed standard treatment. These results are consistent with a variety of other studies demonstrating beneficial effects of CM in improving outcomes of cocaine-abusing patients in drug-free treatment modalities (Higgins et al. 1994
) and in methadone maintenance programs (Silverman et al. 1996
; Griffith et al. 2000
; Petry & Martin 2002
A magnitude effect was noted on some of the outcome measures, with the larger magnitude CM condition generally being more efficacious than the lower magnitude condition. The $240 CM condition was more efficacious than the $80 CM condition with percentage of negative samples submitted. Compared to the $80 CM condition, the $240 CM condition also showed a trend toward engendering longer durations of continuous abstinence. Some other studies have demonstrated magnitude effects when money or vouchers are used as the reinforcer for cigarette (Stitzer & Bigelow 1983
; Stitzer et al. 1986
) or cocaine abstinence (Silverman et al. 1999
). The $80 CM condition, in contrast, did not improve outcomes significantly relative to standard treatment.
Beneficial effects of CM did not extend to other indices of psychosocial problems as measured by ASI composite scores. While time effects were noted on many of the ASI composite scores, no group or group × time interactions emerged. Similar results are noted in other CM studies, which generally find that beneficial effects of CM are limited to the behavior that is targeted (Higgins et al. 1994
; Petry 2000
). Compliance with goal-related activities was reinforced in this study, and patients earned slightly over half their draws for activity completion. Perhaps because goals and activities were individualized, group effects of CM on reducing psychosocial problems were not evident. Some patients focused on enhancing family relationships, while others improved health or legal status. Given that such a range of activities was reinforced, significant effects of CM on ASI composite scores would be difficult to detect.
In CM studies that reinforce only abstinence, 30–50% of patients never access the reinforcer (Stitzer, Iguchi & Felch 1992
; Silverman et al. 1996
; Iguchi et al. 1997
). Reinforcing activity compliance was included to increase the probability that patients would earn reinforcement. All but two patients in the CM conditions earned at least one draw during treatment, and all but four (95%) won at least one prize. While most all patients assigned to a CM condition earned at least some reinforcement, dismantling designs are needed to address whether the beneficial effects are related to the reinforcing abstinence, compliance with activities or the two behaviors concurrently.
Most studies of CM conducted in non-methadone maintained samples find beneficial effects on retention in treatment (see Petry 2000
for review). No differences in retention were noted across groups in the present study, and only a minority of patients remained in treatment for the full 12 weeks. The lack of group differences may be related to the lower overall magnitude of reinforcement used in this study compared with voucher studies. It may also be related to the implementation of this study in community-based clinics, as opposed to research-based treatment centers in which patient case-loads are substantially lower (Higgins et al. 1993
). Regardless of the reason, the similar retention rates noted across groups in this study suggest that any group-related differences in abstinence are not a reflection of greater retention in treatment or the number of urine samples submitted.
Preston et al. (1998)
noted that methadone-maintained cocaine-using patients who initiated CM treatment with cocaine-negative urine samples were more likely to benefit from the experimental treatment than those who initiated CM treatment with positive samples. The present study found a somewhat similar effect in a drug-free treatment setting. Patients who initiated treatment with a cocaine-negative urine sample provided a higher percentage of cocaine-negative urine samples throughout treatment than patients who initiated treatment with a cocaine-positive urine sample.
An interesting interaction effect emerged in this study. The CM treatment was most beneficial for the patients who were least likely to do well in standard treatment— those who initiated treatment with positive urine specimens. Patients initiating treatment with a positive urine sample provided a 4–5 times higher percentage of negative samples during treatment if they received the $240 CM treatment than if they received standard treatment. Intermediary effects were noted in the $80 CM condition, which fared about twice as well as the standard condition in terms of percentage of negative samples. In contrast, those who initiated treatment with a negative urine specimen did relatively well in treatment regardless of whether or not they received CM, with about 89–94% of the urine specimens submitted being drug-free. The lack of a beneficial effect of CM among patients who entered treatment abstinent may be related to a ceiling effect, as few of these patients submitted positive urine specimens during treatment.
If replicated in other settings and with larger samples, these data may suggest that, in a time of cost constraints, CM treatments should be aimed primarily at cocaine-using patients who initiate drug-free treatment with positive samples. The average cost of prizes won by patients in the high magnitude CM condition was $86, and significant reductions in cocaine use were noted with this level of reinforcement. Although other costs including urine testing and personnel time to purchase prizes are associated with CM, the direct costs appear low, especially in relation to voucher CM procedures. (See Petry & Martin 2002
for a discussion of the advantages and disadvantages of the prize CM system relative to the voucher CM system.) By including aspects of the voucher system such as allowance for patient preferences, access to high magnitude rewards and bonuses for continuous abstinence, the prize CM system was successful in engendering beneficial effects among patients who otherwise do poorly in treatment.
Given these relatively low costs, implementation of prize reinforcement CM may be possible in community clinics. Although an average cost of $86 per patient may still be considered prohibitive in some settings, clinics can solicit prize donations from retailers (Amass 1997
). If the interaction effect between baseline drug use and efficacy of CM is replicated in prospective studies then CM, and especially higher magnitude CM, could be applied only to the patients most likely to benefit from them. Finally, societal costs associated with cocaine abuse may far exceed the costs of prizes, or even hundreds to thousands of dollars in vouchers, provided by CM treatments. Larger studies, conducted at sites across the country, are ongoing to evaluate the cost–effectiveness of CM in terms of impact on criminal activity, unemployment and medical sequelae related to drug abuse. Finally, future work must also address training therapists to administer the techniques and the efficacy of the procedures when administered by community-based therapists.
Long-term evaluations of CM on drug use as well as other psychosocial outcome measures are also necessary. Higgins, Badger & Budney (2000b)
found that the longest duration of continuous abstinence during treatment is a significant predictor of 6-month outcomes. In a study of prize reinforcement CM in methadone patients, beneficial effects of CM were maintained for 2 months following the removal of the reinforcement (Petry & Martin 2002
). Although beneficial effects of this CM system were noted in the short term, the majority of patients did not remain in treatment for the full 12 weeks of this study. Strategies to enhance treatment participation and improve outcomes over longer periods of time need to be investigated. These may include booster CM sessions or a longer duration of CM treatment with reductions in probability of reinforcement once substantial periods of abstinence have been achieved (e.g. Kirby et al. 1998
). CM procedures may also be useful to enhance participation in other forms of treatment that have more enduring effects, such as cognitive–behavioral therapy (Carroll et al. 1994
In summary, this study provides further evidence of the efficacy of this prize reinforcement CM procedure for reducing drug use in community-based, drug-free substance abuse treatment programs. Additional research is needed to evaluate the cost–effectiveness of this approach and to delineate important parameters, such as the probabilities of reinforcement, optimal durations of treatment and targets of reinforcement, under which these procedures engender beneficial effects, and the patients for whom the procedures are most beneficial and cost effective.