CRD summary

This review concluded that contingency management methods promote abstinence from alcohol, tobacco and illicit drugs during the treatment of substance use disorders. Evaluation of the reliability of the authors' conclusions is not possible given their informal assessment of the validity of the included studies, high attrition rates, and the unknown influence of studies contributing more than one comparison to the review.

Authors' objectives

To evaluate the effectiveness of contingency management (CM) methods during the treatment of substance use disorders.

Searching

Current Contents, BIOSIS Previews, EMBASE, MEDLINE, PsycINFO, Sociological Abstracts, the Project CORK database, and the Cochrane Library were searched for studies published in the English language from 1970 to 2002; the search terms were reported. The reference lists of retrieved documents were examined for additional studies.

Study selection

Assessment of study quality

The authors did not state how they assessed validity. The authors stated that the included studies were high quality because most were randomised, were conducted in controlled settings, and were funded by the National Institute on Drug Abuse or a Public Health Service agency, indicating that the designs met peer-review standards.

Data extraction

One of five trained, masters- or doctoral-level coders extracted data using a pilot-tested codebook. They met regularly with senior staff; an expert in CM reviewed coding for accuracy. Any discrepancies were resolved by consensus among coders and senior investigators.

Drug use was computed as an average of multiple measures taken during treatment, or as a single measure at the end of treatment. A standardised mean difference effect size (ES) and corresponding 95% confidence interval (CI) were computed for each comparison by extracting the treatment and control group means and pooling the standard deviations, or by using reported t, F, or chi-squared statistics. When proportions were reported, the ES was based on arcsine transformations of treatment and control group proportions. When sample sizes were small, a correction factor was applied. If drug use was reported after treatment had ended, an average ES was computed for each quarter after treatment, up to 12 months.

Data were extracted for potential moderators of ES; these included the decade in which a study was conducted, involvement of the researcher with respect to design and delivery of the intervention, drug targeted for reinforcement of abstinence, and planned duration of the intervention.

Methods of synthesis

Results of the review

Forty-four treatment-control group studies (baseline n=4,652) were included providing 47 treatment-control comparisons: 40 studies were experimental (baseline n=3,409) and 4 studies were quasi-experimental (baseline n=1,243).

Attrition ranged from 0 to 65%.

CM methods were more effective than no treatment or standard treatment in promoting and sustaining abstinence from psychoactive substances: the ES was 0.42 (95% CI: 0.35, 0.50) when using a fixed-effect model and 0.49 (95% CI: 0.38, 0.59) when using a random-effects model. Evidence for statistical heterogeneity was significant for fixed treatment effects (p<0.05) and non significant for random treatment effects.

Analyses of follow-up data suggested a general downward trend in CM effectiveness after the end of treatment. However, the estimates were based on a small sample of studies (range: 2 to 6) for each quarter following treatment.

The ES was greater for studies conducted during the 1970s to 1980s versus the 1990s (p<0.01) and for studies where the researcher was more involved versus less involved in designing or delivering the intervention (p<0.01). The ES also varied with target drug (p<0.04) (greater ES for treating opiate or cocaine use versus tobacco use) and treatment duration (p<0.03) (greater ES for shorter treatment duration).

The authors investigated the effect of study features on overall ES estimates by omitting quasi-experimental designs and self-reports; in both cases the ES increased (p<0.05). They also compared mean during-treatment ES and end-of-treatment ES (non significant difference).

The trim-and-fill analysis suggested that 15 comparisons favouring the control group were needed to offset possible publication bias. The addition of imputed negative values to the meta-analyses reduced the estimated effectiveness of CM: the adjusted ES was 0.27 (99% CI: 0.21, 0.34) when using a fixed-effect model and 0.29 (99% CI: 0.17, 0.42) when using a random-effects model.

Authors' conclusions

CM techniques are effective in promoting abstinence from alcohol, tobacco and illicit drugs during the treatment of clients with substance use disorders. CM enhances standard treatment by establishing and maintaining abstinence, thereby facilitating client participation in other aspects of clinical services.

CRD commentary

This review addressed a well-defined research question in terms of the population, intervention, outcome and study design. Control groups were broadly defined as receiving non-CM. Some of the included control groups received no treatment or standard treatment, and some received non-contingent reinforcement (NCR). It is unclear if NCR was considered standard treatment. Differences in the treatment of control groups could have biased overall estimates of CM effects. For example, the magnitude of an effect might depend on whether the control group received reinforcement. If so, the overall estimate would be affected by the distribution of control group types.

Relevant databases were searched and the search terms were reported. All of the included studies were published in English, possibly introducing language and publication bias. To assess potential publication bias, reanalyses were conducted with the addition of imputed values. The adjusted values for ES were smaller, but still positive. Coders identified ineligible studies and senior researcher staff confirmed their decisions. Data extraction errors were controlled by careful coding procedures. Although the authors described the studies as high quality, study validity was not assessed. Substantial attrition in several studies might have led to an overestimation of the treatment effect. Three studies contributed two comparisons each; the influence of these studies was not investigated.

Meta-analyses using fixed-effect and random-effects models were conducted. The random-effects model may have been more appropriate given the variety of CM reinforcers, substances targeted, and evidence for statistical heterogeneity of the fixed effects. Post-hoc contrasts in the analyses of moderators of CM were tested at the 0.05 level of significance, perhaps inadequately controlling for Type I errors that lead to false conclusions of significance.

It is difficult to evaluate the reliability of the main conclusion regarding the effectiveness of CM, owing to the informal assessment of the validity of individual studies, the high attrition rates for several studies, and the unknown influence of studies contributing more than one comparison to the review.

Implications of the review for practice and research

Practice: The authors stated that CM enhances the effectiveness of standard treatment by establishing and maintaining abstinence, which in turn improves client participation in other aspects of clinical treatment. However, the effect of abstinence on participation was not investigated in this review. The usefulness of CM as a stand-alone treatment is not known. For clients with severe problems, continued care following the end of CM is justified.

Research: The authors stated that future research should compare CM types, CM with other treatments of substance use disorders, and moderators of CM.

Funding

Program Evaluation and Resource Center, VA Palo Alto Health Care System, contract V261P-1447; National Institute on Drug Abuse, grant numbers R01-DA017407 and R01-DA017084.

Bibliographic details

Prendergast M, Podus D, Finney J, Greenwell L, Roll J. Contingency management for treatment of substance use disorders: a meta-analysis. Addiction 2006; 101(11): 1546-1560. [PubMed: 17034434]

Indexing Status

Subject indexing assigned by NLM

MeSH

Behavior Therapy /methods; Humans; Substance-Related Disorders /therapy; Treatment Outcome

AccessionNumber

12006007659

Database entry date

31/12/2007

Record Status

This is a critical abstract of a systematic review that meets the criteria for inclusion on DARE. Each critical abstract contains a brief summary of the review methods, results and conclusions followed by a detailed critical assessment on the reliability of the review and the conclusions drawn.