Abstract BACKGROUND: Randomized controlled trials are considered the best scientific proof of effectiveness. There is increasing concern, though, about their feasibility in psychotherapy research. We discuss a quasi-experimental study design for situations in which a randomized controlled trial is not feasible. Here, as an alternative strategy, the propensity score (PS) method is used to correct for selection bias. METHODS: We used data from a Dutch research project, SCEPTRE (Study on Cost-Effectiveness of Personality Disorder Treatment). The sample consisted of 749 psychotherapy patients with personality pathology. We tested whether the PS method was useful and applicable. We examined differences between 2 treatment groups (short vs. long treatment duration) in pretreatment characteristics before and after PS correction. This revealed the impact of the PS on outcome differences. RESULTS: The PS offered statistical control over observed pretreatment differences between patients in a non-randomized study. CONCLUSIONS: When a randomized controlled trial is not possible, this quasi-experimental design using the PS could be a feasible alternative. Its advantages and limitations are discussed. Implemented carefully, this method is promising for future effectiveness research.

Psychotherapy, Quasi-experiment, Randomized controlled trials, selection bias, Research design, propensity score
dx.doi.org/10.1159/000162298, hdl.handle.net/1765/23041
Psychotherapy and Psychosomatics
Erasmus MC: University Medical Center Rotterdam

Bartak, A, Spreeuwenberg, M.D, Andrea, H, van Busschbach, J.J, Croon, M.A, Verheul, R, … Stijnen, Th. (2008). The Use of Propensity Score Methods in Psychotherapy Research. Psychotherapy and Psychosomatics, 78(1), 26–34. doi:10.1159/000162298