We have noted that the successful development and implementation of a new behavioral treatment can be conceptualized as progressing through several stages of science, to dissemination and, finally adoption. Also noted is the failure of this progression and the resulting gap between research and practice in the substance abuse treatment (Lamb, Greenlick & McCarty, 1998
). Numerous behavioral therapies have demonstrated efficacy in treating substance abuse however considerably fewer effectiveness trial outcomes are available. The NIDA CTN is one of the largest and most recent national efforts to conduct effectiveness trials of drug abuse treatment in community treatment settings. We have used four examples of trials developed in the CTN, to examine important considerations in choosing a control group. The complexity of clinical trial design increases considerably when moving from a single-site study at a carefully controlled research clinic to a community-based treatment program with a primary mission to deliver clinical care. These conditions may be further complicated in the case of multi-site effectiveness trial, where each site has unique characteristics that may interact with the new treatment. Community-based effectiveness trials are ultimately useful when the treatments being tested are applied and shown to work in practice. The more representative the sites in the study are of the range of actual settings and practices in the community the greater the generalizability of the results.
As with many aspects of clinical trial design, choice of a control group is largely driven by the key research question the trial is designed to answer. For example: What is the central question about treatment that the proposed clinical trial is being designed to answer? What is the right question to ask given the stage of scientific knowledge about the treatment being investigated? What are the needs of the treatment community and patients?
Our examination of the four designs presented here leads us to view the merits and compromises of each control group along a continuum from internal to external validity. As the choice of control increased in ecological validity it decreased in internal control.
We recommend the following considerations when choosing a control group or when interpreting the results of effectiveness trials. First, what is the strength of prior evidence for the efficacy of the intervention. If strong efficacy data are available investigators may be much less concerned with evaluating the treatment specific effects of the new intervention. In this situation the importance is placed on providing the most compelling evidence for adoption of the new intervention if the results show it to be superior and designs 1 & 2 may be the most desirable. However, if strong efficacy data are not available, or if the new treatment is modified from the version tested in previous efficacy studies, there may remain a need to establish the efficacy of the intervention. As a result the design may benefit from greater internal control to ensure the observed difference are specific to the new treatment and not due to non specific factors such as the amount of attention given to patients. In this circumstance designs 3 & 4 may provide more appropriate comparisons. A second recommendation is to consider the degree to which the control group provides a comparison that is useful to providers who are ultimately the adopters of the new treatment. Here the more representative the control condition is of the most common clinical practices the more easily the results can be interpreted by providers. In the case of designs 1 & 2 a direct comparison to TAU is provided and the results are easily understood. The provider can easily see the new treatment was inferior, equal, or superior to their practice depending on the results of the trial. Design 3 also incorporates TAU and provides a useful comparison however since neither condition is TAU only the interpretation is not as direct. Design 4 provides the least amount of information regarding a direct comparison with current practice. A final recommendation is to give careful consideration to what constitutes current treatment settings. Providing evaluation of new treatments in settings representative of those in which interventions will ultimately be adopted, provides the strongest support for adoption when the intervention is demonstrated to be effective. This approach anticipates the next set of questions in the process of moving from science to practice. These questions are posed by the providers; is this new treatment an improvement over my current practice, can I adopt it and, should I adopt it?