Enhancing the validity and utility of randomized clinical trials in addictions treatment research: II. Participant samples and assessment.

Purpose: This paper is the second in a series that describes strategies for optimizing the validity and utility of randomized clinical trials (RCTs) in addictions treatment research. Whereas the first paper focused on treatment implementation and research design, here we address issues pertaining to participant samples and assessment methods.

Scope: With respect to participant samples, sections focus on the definition of study populations; informed consent; sample size and statistical power; recruitment and enrollment; sample retention; and participant tracking systems. Assessment topics include eligibility screening and baseline assessment; treatment-related variables; outcome measures; the frequency of follow-up evaluation; and assessment process. A final section highlights the importance of pilot testing.

Conclusions: Sample recruitment and retention strategies are needed that safeguard both internal and external validity. Daily estimation assessment procedures are recommended because of their versatility for creating a range of outcome measures. Assessment batteries should include measures that permit the investigation of treatment processes and mechanisms of action.