PROSPERO is the international prospective register of systematic review protocols, hosted by the Centre for Reviews and Dissemination at the University of York on behalf of the National Institute for Health and Care Research. Launched in 2011 and free to use, it is the largest and most established protocol registry for systematic reviews of healthcare interventions, public health, social care, education, and clinical research.
A PROSPERO record is a structured, publicly searchable description of a planned systematic review, submitted before screening begins or at the latest before data extraction. Once approved, the review receives a unique PROSPERO identifier that journals, peer reviewers, and funders use to verify that the published review matches the registered plan. This guide covers what PROSPERO does, why it exists, who can use it, what review types are eligible, and how it fits alongside alternatives like the Open Science Framework and INPLASY.
Why Prospective Registration Reduces Bias in Systematic Reviews
Prospective registration solves a problem that took the systematic-review community two decades to articulate. Without registration, reviewers can change inclusion criteria, switch primary outcomes, or modify the analysis plan after seeing the data. These post-hoc changes look reasonable at the manuscript stage but can introduce outcome-reporting bias and inclusion bias that are invisible to peer reviewers. The mechanism is the same as in clinical trials, where the move to mandatory prospective registration on ClinicalTrials.gov reduced the gap between planned and reported outcomes.
PROSPERO addresses the analogous problem in evidence synthesis. By making the planned review question, eligibility criteria, search strategy, and synthesis methods publicly visible before any screening happens, the registry creates a credible record against which the finished review can be compared. Editors, methodologists, and peer reviewers can pull the original PROSPERO record and ask whether the manuscript matches the plan or has drifted from it without disclosure.
A second purpose of PROSPERO is deduplication. Hundreds of systematic reviews are started every week worldwide, and many overlap. A reviewer who searches PROSPERO before committing to a question can discover that a similar review is already underway and either join it, change scope, or wait for the existing review to publish. This avoids wasted effort and reduces redundant publications cluttering the literature.
What a PROSPERO Record Contains
A PROSPERO submission collects a fixed set of structured fields. The review question and objectives describe what the review aims to answer. The PICO elements, when applicable, define the population, intervention, comparator, and outcomes. The eligibility criteria specify which study designs, settings, and patient populations are included or excluded. The search strategy lists the databases and date ranges to be searched, with as much specificity as the reviewers can offer at registration. The methods of synthesis outline the planned approach to data extraction, risk of bias assessment, and quantitative or narrative synthesis.
The record also captures administrative metadata: the review team and their institutional affiliations, the funder, conflicts of interest, the anticipated start and completion dates, and a contact author who is responsible for keeping the record current. The contact author is the named point of contact for editors and readers, and is also responsible for submitting amendments and recording deviations.
PROSPERO is publicly searchable. All approved records appear in the registry's search interface at crd.york.ac.uk/prospero. This visibility is part of the deduplication function: anyone planning a review can look up whether a similar protocol is already registered. It is also part of the accountability function: a finished review's PROSPERO ID lets any reader pull the original protocol and compare.
Eligible Review Types and the Scoping Review Exception
PROSPERO accepts a defined set of review types and explicitly excludes others. Systematic reviews of interventions, exposures, prognostic factors, prevalence, and methodology are eligible. Rapid reviews that follow systematic methodology with abbreviated steps are eligible. Umbrella reviews that synthesize existing systematic reviews are eligible. Diagnostic test accuracy reviews and prognostic reviews are eligible.
Scoping reviews are not eligible for PROSPERO. This is a deliberate scope decision: scoping reviews have a different methodological purpose (mapping a field rather than answering a focused question), and their protocols are not well-suited to the PROSPERO record structure. Scoping review protocols are typically registered on the Open Science Framework at osf.io instead, where the open structure of OSF accommodates the broader format. The systematic review fundamentals primer covers the conceptual distinction between systematic and scoping reviews.
Methodological reviews are eligible if they follow systematic-review methodology. Living systematic reviews are eligible and are tagged in the registry to alert readers that the record will be updated. Network meta-analyses are eligible. Individual participant data reviews are eligible.
Eligible Protocol Stage: When You Must Register
PROSPERO accepts registrations at any point before data extraction begins. The strongest case for accountability is registration before any screening, when no studies have been read in full text and the team cannot have been influenced by what was found. Registration at title-and-abstract screening or even at full-text screening is still accepted, but later registrations are less protective against bias and the record will indicate the stage at which registration occurred.
Registration after data extraction begins is not accepted. This rule exists because at that point the team has read the included studies in detail and could be influenced by what they have seen when defining the analysis. A protocol registered after data extraction cannot credibly claim to be prospective.
Reviewers occasionally try to register after the review is well underway, sometimes after a journal editor asks for a PROSPERO ID at peer review. In those cases the registry will accept the submission only if data extraction has not started, will record the actual stage at registration, and will note that registration was not fully prospective. Reviewers in this situation are usually better served by registering on the Open Science Framework, which has no eligibility stage requirement, and explaining the timing in the methods section.
How the Registration and Approval Process Works
A PROSPERO submission is reviewed by the registry's editorial team before approval. The reviewers check that the submission is complete, that the review question is appropriate for systematic review methodology, that the review type is eligible, that the team has not already registered the same protocol, and that the planned methodology is internally consistent. They do not assess scientific merit or pre-judge the conclusions.
The typical timeline is two to four weeks from submission to approval. The actual time depends on registry workload, the completeness of the initial submission, and any queries that the editorial team raises. Common reasons for delays or queries include incomplete eligibility criteria, vague search strategies, mismatch between the stated review type and the planned methods, and confusion about whether the review is truly systematic. The step-by-step PROSPERO registration walkthrough covers the submission interface and the most common queries reviewers receive.
Once approved, the registration receives a unique PROSPERO identifier in the format CRD42024xxxxxx. This ID is what reviewers cite in the manuscript and in correspondence with journals. The record is then publicly visible and remains so indefinitely. The registry does not delete records, even if the review is abandoned or withdrawn. This permanence is what makes PROSPERO usable for accountability purposes.
