Objective: While randomized clinical trials offer high internal validity, their generalizability to real-world practice is often limited due to ethical and/or legal problems with experimental manipulations, especially the assignment of participants to waiting lists or placebo conditions. The quasi-experimental multiple baseline panel design (QE-MBPD) is introduced as a viable alternative to randomized clinical trials for evaluating psychotherapy outcomes in routine clinical settings.

Method: The QE-MBPD adapts the traditional single-subject multiple baseline design to larger groups, thereby increasing possibilities for statistical analysis and generalizability. In the quasi-experimental version proposed, natural variation in clinic waiting times is utilized to establish varying baseline lengths, which is crucial for the internal validity of the design.

Results: The article outlines the principles, applications, advantages, and limitations of the QE-MBPD, emphasizing its potential to bridge the gap between academic research and regular clinical practice. An ongoing empirical study in Swedish community-based psychiatric care is used to demonstrate the design's effectiveness and versatility. We also explore the potential of QE-MBPD to enhance routine outcome monitoring systems by using deviations from the projected trend, established during the baseline phase, as criteria for determining when feedback should be provided during the treatment phase.

Conclusions: Despite the strengths of the QE-MBPD, the reliance on a waiting-list phase as control condition is a principal limitation, similar to what has been argued in randomized clinical trials. There is a need for further research to fully establish the strengths and weaknesses of this design in advancing evidence-based psychotherapy practice.