An a priori systematic review protocol is important because it pre-defines the objectives and methods of the systematic review. A review protocol provides the plan or proposal for the systematic review. Any deviations from the review protocol should be discussed in the systematic review report. 

The review protocol describes:

  • the context and rationale for the review, including what is already known and uncertainties,
  • the study selection criteria (inclusion/exclusion criteria),
  • the outcome measures, interventions, and comparisons considered,
  • the proposed search strategy for identifying relevant studies,
  • the procedures for study selection,
  • the critical appraisal process and instruments,
  • the data extraction process and instruments,
  • the process for resolving disagreement between reviewers in study selection,  data extraction, and critical appraisal decisions, and
  • the proposed approaches to synthesis