Eligible study designs should be stated here, along with any thresholds for inclusion based on the conduct or quality of the studies. For example, ‘All randomised controlled comparisons’ or ‘All randomised controlled trials with blind assessment of outcome’. Exclusion of particular types of randomised studies (for example, cross-over trials) should be justified.
It is generally for authors to decide which study design(s) to include in their review. Some reviews are more restrictive, and include only randomized trials, while others are less restrictive, and include other study designs as well, particularly when few randomized trials addressing the topic of the review are identified. For example, many of the reviews from the Cochrane Effective Practice and Organization of Care (EPOC) Collaborative Review Group include before-and-after studies and interrupted time series in addition to randomized and quasi-randomized trials.