Evidence synthesis researchers are strongly encouraged to develop a project protocol prior to substantive searching and selection of literature or other aspects of the project. In the same way that a protocol serves as a plan or roadmap for experimental research, an evidence synthesis protocol serves as a plan or roadmap for this type of research and, importantly, helps reduce bias in the selection of included studies.
Chapter 1 of the Cochrane Handbook for Systematic Reviews of Interventions offers guidance on the rationale for doing so:
Preparing a systematic review is complex and involves many judgements. To minimize the potential for bias in the review process, these judgements should be made as far as possible in ways that do not depend on the findings of the studies included in the review. Review authors’ prior knowledge of the evidence may, for example, influence the definition of a systematic review question, the choice of criteria for study eligibility, or the pre-specification of intervention comparisons and outcomes to analyse. It is important that the methods to be used should be established and documented in advance.
Publication of a protocol for a review that is written without knowledge of the available studies reduces the impact of review authors’ biases, promotes transparency of methods and processes, reduces the potential for duplication, allows peer review of the planned methods before they have been completed, and offers an opportunity for the review team to plan resources and logistics for undertaking the review itself.
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Reporting guidelines can help you make sure you include all the necessary elements in your written protocol. The widely-accepted PRISMA (Preferred Reporting Items for Systematic Review and Meta-analyses) guidelines offer an extension specifically for protocols, PRISMA-P. Use the protocol guide to make sure you address all the necessary components of an evidence synthesis protocol.
Cochrane's MECIR (Methodological Expectations of Cochrane Intervention Reviews) Manual also includes a section on protocol development.
Protocols will likely contain most or all of the following elements:
Some publication venues will require that protocols be registered (e.g., Cochrane Reviews). Even if you are not required to register your protocol, registration can "stake your claim" to work on that question topic. There are other benefits to developing and registering a protocol, including increased review quality (Sideiri et al., 2018) and limiting duplication of evidence synthesis research efforts.
Some protocol registration options include the following websites.
Discipline-agnostic
Discipline-specific
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