Systematic Review Registration and Protocols

A protocol fixes the review's question, eligibility criteria, outcomes and analysis plan before the results of the included studies are known. Registering it publicly is what lets editors and reviewers check that the published review answered the question it set out to answer, rather than the one that produced the most interesting result.

Most health journals now expect registration, and many ask for the registration number at submission. PROSPERO, run by the Centre for Reviews and Dissemination at the University of York, is free and widely recognised for reviews with a health-related outcome, but it does not accept scoping reviews and its processing time varies. INPLASY charges a fee and publishes registrations quickly. The Open Science Framework accepts protocols of any type. The right choice depends on the review type, the target journal and the timeline.

Timing matters as much as the registry. Registration should happen before screening against eligibility criteria begins; a record created after data extraction invites the question of whether the plan was shaped by the data. PRISMA-P sets out what a protocol should contain, and following it makes the later PRISMA 2020 report much easier to write, because the methods section largely already exists.

Reviewers check registration in specific ways. They compare the registered outcomes with the reported ones, look for undeclared changes to eligibility criteria, and note when the registration date falls after the search date. None of this is a problem when changes are recorded openly with a reason and a date; it becomes one when a discrepancy is discovered rather than declared, because it then reads as selective reporting.

The notes in this topic compare registries side by side, explain what to put in each field, show how to record and justify amendments when the plan has to change, and describe how reviewers compare a registered protocol with the final manuscript.