Analyzing data from open enrollment groups: current considerations and future directions.

Difficulties in modeling turnover in treatment-group membership have been cited as one of the major impediments to ecological validity of substance abuse and alcoholism treatment research. In this review, our primary foci are on (a) the discussion of approaches that draw on state-of-the-science analytic methods for modeling open-enrollment group data and (b) highlighting emerging issues that are critical to this relatively new area of methodological research (e.g., quantifying membership change, modeling "holiday" effects, and modeling membership change among group members and leaders). Continuing refinement of new modeling tools to address these analytic complexities may ultimately lead to the development of more federally funded open-enrollment trials. These developments may also facilitate the building of a "community-friendly" treatment research portfolio for funding agencies that support substance abuse and alcoholism treatment research.