[Algorithm for Choosing the Study Design in Systematic Reviews]

Background: The Federal Joint Committee (Gemeinsamer Bundesausschuss) assigns the highest evidence level of Ia to systematic reviews of randomized controlled trials in evaluating the benefit of therapeutic interventions. Contradictory results among randomized and non-randomized studies may not always be caused by the study design. Methods: The objective of the study was to identify statements in systematic or non-systematic reviews about the choice of study designs in systematic reviews. Another objective was to develop an algorithm to facilitate the choice of appropriate study designs in systematic reviews. Results: The inclusion of non-randomized in addition to randomized study designs was supported by 85% of the 42 identified articles. A strong reason was the need to evaluate the possible treatment-associated harm. The developed algorithm included the 4 decision points of length of follow-up, frequency of events, outcomes, and study designs. Conclusions: If the benefit and the harm of a therapeutic intervention is planned to be evaluated, then often multiple study designs are required to be included. The algorithm provides guidance on which study designs should be considered for inclusion in systematic reviews.