Figure 1

Algorithm for inclusion/exclusion of reviews. Screening algorithm (based on inclusion criteria as per Table 1). Each decision point has the three options for promoting records to the next stage of the winnowing process: ‘yes’ (inclusion), ‘no’ (exclusion), ‘maybe’. Depending on the stage of the reviewing process (on title and abstract only, or full text), the latter option may require retrieving the full text, discussion between reviewers, and/or referral to a third reviewer.