Generally speaking the editorial group expect the inclusion of studies to be confined to controlled clinical trials and randomised controlled trials. However, the scope of the group is such that there may be problems where interventions are difficult to evaluate using experimental methodology and, in these cases, reviewers are asked to make the case for extending inclusion criteria to other forms of study design in the development of the protocol.
The group requires the inclusion criteria developed for a review to be applied independently by at least two review authors for each potentially relevant study. Disagreements that cannot easily be resolved are referred to a third author, and/or a member of the editorial team. Studies that, in the judgement of the review authors, are seriously compromised by weaknesses in design, conduct or analysis are excluded. Details of such studies are reported in the 'Characteristics of excluded studies' tables within reviews.
Assessment of methodological quality
The policy of the CDPLP is that all review authors should develop a data extraction sheet tailored to their own reviews (see here for templates). At least two review authors should extract data independently for each review. In the event the report of a trial lacks relevant information (method of randomisation, data) study authors should be contacted for further details. Review authors should seek help from the editorial base in contacting study authors if this proves difficult.
Core guidance is available in the Cochrane Handbook for Systematic Reviews of Interventions.