Fig 2. Systematic or non-systematic process used by guidelines in their approach to evidence synthesis (n = 50).

To determine if a systematic process was used to gather, assess and synthesise evidence to inform recommendations, we used the following four criteria: (1) explicit statement of the questions or objectives reported in terms of PICOS (Populations, Interventions, Comparisons, Outcomes, and Study design) elements; (2) eligibility criteria reported for all included study designs; (3) a systematic search conducted (i.e. two or more databases searched); and (4) process reported for selecting/screening studies (e.g. number of authors, independent process). We considered these criteria to be the minimum that can be used by a guideline to reduce bias and limitations when gathering evidence to inform recommendations.