The effectiveness and ineffectiveness of complex behavioral interventions: impact of treatment fidelity.

There is often wide variability in the reported effects of complex behavioral interventions. Effectiveness can vary across studies, sites, and providers. A factor that has been insufficiently considered is the fidelity of the behavioral treatment that was provided. Low quality practice could be likened to partial doses of a vaccine or antibiotic: the right idea but insufficient strength. Using motivational interviewing (MI) as an example, the authors describe three quality conditions that should be present for a study to be regarded as a trial of a complex behavioral intervention: (1) The treatment should clearly contain the components that are theoretically or empirically related to its efficacy; (2) providers should be trained to an adequate and specified criterion of proficiency before treating trial patients; and (3) the fidelity of treatment should be documented by reliable coding of practice throughout the study and reported in a manner that permits comparison with skill levels in other trials. The authors also discuss bona fide intervention failures despite strong clinical trial methodology, offering recommendations for future outcome research.