Systematic reviewers generally separate the study selection process into two stages: (1) a broad screen of the titles and abstracts of the citations retrieved from the literature search, and (2) a strict screen of the full-text articles passing the broad screen to select the final included studies. Both phases of this selection are facilitated through the use of eligibility criteria. Pilot testing the eligibility criteria on a random sample of citations and/or full-text articles can be conducted to ensure that study relevance is assessed consistently across reviewers. The reviewers should check realiability of the eligibility criteria by measuring the percent agreement or kappa statistic; the reviewers should only proceed if there is good agreement (>90%) for the eligibility criteria. The process of identifying and selecting studies requires detailed recordkeeping because it must be reported in sufficient detail for the end user to determine validity.