Note that outcome measures do not always form part of the criteria for including studies in a review. If they do not, then this should be made clear. Outcome measures of interest should be listed in this section whether or not they form part of the inclusion criteria.
For most reviews it will be worthwhile to pilot test the inclusion criteria on a sample of articles (say ten to twelve papers, including ones that are thought to be definitely eligible, definitely not eligible and questionable). The pilot test can be used to refine and clarify the inclusion criteria, train the people who will be applying them and ensure that the criteria can be applied consistently by more than one person.
Even when explicit inclusion criteria have been specified, decisions concerning the inclusion of individual studies remain relatively subjective. There is evidence that using at least two authors has an important effect on reducing the possibility that relevant reports will be discarded (Edwards et al. 2002). Agreement between assessors may be formally assessed mathematically using Cohen's Kappa (a measure of chance-corrected agreement). Many disagreements may be simple oversights, whilst others may be matters of interpretation. These disagreements should be discussed, and where possible resolved by consensus after referring to the protocol. If disagreement is due to lack of information, the authors may have to be contacted for clarification. Any disagreements and their resolution should be recorded.
The influence of uncertainty about study selection may be investigated in a sensitivity analysis.
It is useful to construct a list of excluded studies at this point, detailing the reason for each exclusion. This list may be included in the report of the review as an appendix. The final report of the review should also include a flow chart or a table detailing the studies included and excluded from the review. In appendix a flow chart is provided for documenting study selection. If resources and time allow, the lists of included and excluded studies may be discussed with the expert panel. It may be useful to have a mixture of subject experts and methodological experts assessing inclusion.