When wait lists are not feasible, nothing is a thing that does not need to be done

Clinical psychology practices initially grew through the use of case studies, uncontrolled trials, and eventually through randomized controlled trials (RCTs). The use of a wait-list control group is standard practice in such trials of treatment regimens for psychopathological conditions. However, as knowledge advances regarding the successful treatment of such conditions, best practice guidelines are being developed. These guidelines have predominantly been based on the results of RCTs and use aggregating mechanisms, such as meta-analysis, to derive their conclusions. The authors argue here for statistical methods that allow for comparisons to existing data from wait-list controls for which the continued use of wait-list conditions has become problematic. Using posttraumatic stress disorder (PTSD) as an example, this article proposes various methods for obviating the need for a wait-list control under such circumstances. After conducting separate meta-analyses for both treatment and control conditions, the authors found that wait-list conditions do provide some benefit to participants with PTSD, but current best practice treatment conditions elicit far superior effect sizes. The various methods for evaluating a study without a wait-list control are proposed and demonstrated.