Estimating statistical power for open-enrollment group treatment trials.

Modeling turnover in group membership has been identified as a key barrier contributing to a disconnect between the manner in which behavioral treatment is conducted (open-enrollment groups) and the designs of substance abuse treatment trials (closed-enrollment groups, individual therapy). Latent class pattern mixture models (LCPMMs) are emerging tools for modeling data from open-enrollment groups with membership turnover in recently proposed treatment trials. The current article illustrates an approach to conducting power analyses for open-enrollment designs based on the Monte Carlo simulation of LCPMM models using parameters derived from published data from the National Drug Abuse Treatment Clinical Trials Network randomized controlled trial comparing Seeking Safety to a community care condition for women presenting with comorbid posttraumatic stress disorder and substance use disorders (protocol CTN-0015). The example addresses discrepancies between the analysis framework assumed in power analyses of many recently proposed open-enrollment trials and the proposed use of LCPMM for data analysis. Hopefully, this step-by-step power analysis demonstration for data from open enrollment groups will provide researchers within and outside of the behavioral treatments area with guideposts for powerful new trials and secondary analytic projects, which will help further bridge the gap between treatment research and treatment in practice.