Systematic review methodologists have proposed using the Population, Intervention, Comparators, Outcome, Study design, and Time period (PICOST) framework to formulate the systematic review question. The eligibility criteria of studies to be included in the synthesis should extend from the PICOST components. Other characteristics that might be considered in developing eligibility criteria include publication status and language of dissemination. Eligibility should be thoroughly considered, properly defined, and transparently reported to avoid ambiguity in the review process and to inform the validity of the review.
A review protocol, which specifies the systematic review methods a priori, should be developed to decrease the likelihood of biased post-hoc methodological changes and selective outcome reporting. Important elements of the review protocol include details on the methods used for search, retrieval and appraisal of the literature, and data abstraction. The PRISMA checklist can also be used for protocol development and reporting.