A study protocol paper describes, in full detail, how a study will be conducted before its results are known. It states the question, the design, the participants, the interventions, the outcomes, and the analysis plan, so that other researchers can judge the study's quality, reproduce its methods, and later compare its published results with what was originally planned. Publishing a protocol is therefore an act of transparency, not merely a preliminary publication.
Protocol papers are peer-reviewed like other articles, and they are judged on the soundness of the plan rather than on results, which do not yet exist. This guide explains when a protocol paper is appropriate, how to register a study, how to structure the paper, and how peer review and publication work for protocols, including the ethical and practical issues authors most often overlook.
A protocol paper publishes the full plan of a study, usually a clinical trial or a large observational study, before recruitment is complete or results are available. Its purpose is to create a public, peer-reviewed record of what was intended, so that later readers can distinguish planned analyses from analyses chosen after seeing the data. That distinction matters: results that were planned in advance carry more weight than results found by exploring data until something interesting appears.
Protocol papers also help the research community in practical ways. They prevent duplication, because other groups can see that a study is already under way. They allow funders and ethics committees to see that a study is well designed before it consumes resources. And they give the study team itself a fixed reference: when decisions must be made during a long study, the published protocol settles what was agreed, rather than leaving it to memory.
A protocol paper suits studies where the design is complex, the stakes are high, or the risk of selective reporting is real: randomised trials, large cohort studies, and studies whose results will inform guidelines or policy. Many trial journals and funders actively encourage or require protocol publication for such studies, and some journals publish protocols as a dedicated article type with their own instructions.
A protocol paper is less suitable for small exploratory studies whose design will change substantially, for studies already complete, or for work where publishing the plan would compromise the study, for example by revealing an allocation method that must stay concealed from participants. In those cases, registration alone, without a full protocol paper, may provide the public record the study needs. Decide before recruitment begins, because a protocol published after results are known cannot serve its transparency purpose.
Registration means entering the study's key details in a public registry before the first participant is enrolled. For clinical trials, registries include ClinicalTrials.gov and the WHO primary registries; for systematic reviews, PROSPERO serves a similar role. Registration creates a dated, public record of the question, the design, the outcomes, and the eligibility criteria, and most journals require a registration number for trials they publish.
Register early and accurately. Enter the primary outcome exactly as it will be analysed, because changing a primary outcome after registration, without explanation, is one of the reporting problems protocol publication exists to prevent. If the study design changes later, update the registry and explain the change in the protocol paper and in the later results paper. A registry entry that contradicts the protocol paper will be noticed by reviewers, and it will raise questions that are avoidable with consistent updating.
Most protocol papers follow the SPIRIT guidance, a checklist for the content of a clinical trial protocol, and many journals require it. SPIRIT covers the administrative information, the introduction and rationale, the methods, and the ethics and dissemination plans, and using its structure helps authors include everything reviewers expect. Even for studies that are not trials, SPIRIT's logic is a useful model: state the question, justify the design, and describe every decision a reader would need to repeat the study.
Begin with a title that identifies the paper as a protocol and names the study design, and an abstract that summarises the question, design, participants, interventions, outcomes, and status. The introduction should explain the problem, summarise the existing evidence, and justify the study, including why this design answers the question better than alternatives. A protocol whose rationale is thin will struggle in review, because reviewers judge the plan's scientific value without results to compensate for it.
Methods are the heart of a protocol paper, and they must be detailed enough for another team to repeat the study. Describe the setting and eligibility criteria, the recruitment process, the interventions in enough detail to replicate them, and the outcomes with their measurement methods and time points. State the sample size and how it was calculated, including the assumptions behind the calculation, so reviewers can judge whether the study is powered to answer its question.
Describe randomisation and blinding where they apply, including who generates the sequence, who enrols participants, and who assigns them, because these details determine whether bias is controlled. State the data collection and management plan, the statistical methods for the primary and secondary outcomes, and how missing data and protocol deviations will be handled. Vague methods are the most common reason protocol papers are returned for major revision, since a plan that cannot be followed cannot be judged.
A protocol paper must show that ethical approval has been obtained or applied for, naming the committee and the reference number where available, and describe how informed consent will be sought. Explain how participants' confidentiality will be protected, how data will be stored and shared, and what provisions exist for care after the study or for harms that may occur. Reviewers read this section carefully, because a protocol paper is itself a public commitment to how participants will be treated.
Describe the oversight arrangements: who monitors the study, whether a data monitoring committee exists, and under what conditions the study would be stopped early. For studies involving vulnerable participants, children, or sensitive data, explain the additional safeguards in place. If approval is pending at submission, say so honestly and update the paper before publication; a protocol paper published without any ethics statement will not be accepted by reputable journals.
Studies change, and a good protocol anticipates that. State how amendments will be decided, approved, and communicated to ethics committees, registries, and the journal, and how version numbers and dates will be recorded. When the protocol paper itself is updated, explain what changed and why, so that readers comparing versions can follow the study's history rather than discovering unexplained differences.
Distinguish minor amendments, such as clarifying a procedure, from major ones, such as changing an outcome or eligibility criteria, which require fuller justification and approval. Record every amendment, however small, because the cumulative history of a study is part of its scientific record. A protocol that pretends no changes occurred, when the results paper later shows otherwise, damages the credibility of the whole study.
Reviewers of protocol papers judge the plan, not results, so their questions differ from those asked of a results paper. They ask whether the question is important and original, whether the design can answer it, whether the sample size is adequate, whether the outcomes are appropriate and fully defined, and whether the analysis plan is complete and pre-specified. They also check feasibility: can this team recruit these participants, in this setting, within this timeframe, with these resources?
Expect reviewers to challenge the design itself, not merely its description. They may suggest a different comparator, a longer follow-up, or an additional outcome, and those suggestions, made before data collection, can substantially improve a study. Respond to them as you would to any peer review: point by point, with reasons, and revise the protocol where the criticism is sound. A protocol improved by review is worth more than a protocol published unchanged but flawed.
Choose a journal that publishes protocols as an article type and that reaches the audience who will use the study's results. Some journals specialise in protocols, while others accept them alongside other article types; check the author guidelines for protocol-specific requirements, including registration, the SPIRIT checklist, and any requirement to submit the full protocol as supplementary material. A journal that does not publish protocols will desk-reject the paper regardless of quality.
Consider timing. Submitting a protocol paper early, before recruitment is complete, maximises its transparency value and allows review to improve the study while changes are still possible. Submitting after recruitment has finished reduces that value, and submitting after results are known defeats it. Tell the editor the study's status honestly in your cover letter, including the registration number and the recruitment stage, so the paper is assessed on the correct basis.
Publication of a protocol creates an obligation: when results are published, they must be linked to the protocol and any differences explained. Cite the protocol paper in the results paper, report the outcomes exactly as pre-specified, and describe any outcome that was added, dropped, or changed, with reasons. Readers and systematic reviewers compare the two documents, and unexplained differences are treated as a reporting concern.
Keep the protocol accessible. Deposit the full protocol and any amendments where the journal or funder requires, keep the registry entry updated through to completion, and share data and code according to the plan stated in the protocol. A protocol paper that is followed by a results paper that honours it is one of the strongest signals of trustworthy research a team can produce.
Use this checklist before submission: the study is registered and the number is stated; the title identifies the paper as a protocol; the rationale and design are fully justified; methods, outcomes, sample size, randomisation, and analysis are described in repeatable detail; ethics approval and consent are documented; oversight and stopping rules are stated; the amendment process is described; and the study's current status is stated honestly in the cover letter. If any item fails, revise before submitting.
Finally, remember that a protocol paper is a promise made in public, and keeping it is what gives it value. Write it as carefully as you would a results paper, welcome the review that improves it, and honour it when results arrive. For related guidance, see our guide on how to publish a research paper, our methodology guide on how to write a methodology section, and our explainer on open access publishing explained.
| Element | What to include | Common reviewer check |
|---|---|---|
| Registration | Registry name and number | Registered before first enrolment |
| Design | Study type and rationale | Design answers the question |
| Participants | Eligibility and recruitment | Feasible in the stated setting |
| Outcomes | Primary and secondary, with time points | Fully defined, pre-specified |
| Analysis | Sample size and statistical plan | Powered, missing data addressed |
These authoritative external resources explain the standards and tools mentioned in this guide:
What is a study protocol paper?
A study protocol paper publishes the full plan of a study before its results are known, including the question, design, participants, interventions, outcomes, and analysis plan. It creates a public, peer-reviewed record that later readers can compare with the published results.
Must a study be registered before a protocol paper?
For clinical trials, yes: most journals require a registration number from a public registry such as ClinicalTrials.gov, entered before the first participant is enrolled. For systematic reviews, PROSPERO serves a similar role, and registration should likewise precede the work.
What is the SPIRIT statement?
SPIRIT is a checklist for the content of a clinical trial protocol, covering administrative information, rationale, methods, ethics, and dissemination. Many journals require protocol papers to follow it, and its logic is a useful model even for studies that are not trials.
How is a protocol paper peer-reviewed?
Reviewers judge the plan rather than results: whether the question is important, whether the design can answer it, whether the sample size is adequate, whether outcomes are fully defined, and whether the study is feasible. Suggestions made at this stage can still improve the study.
Can a protocol change after publication?
Yes, but changes must be handled formally: approved by the ethics committee, updated in the registry, and explained in later publications. Major changes, such as altering a primary outcome, require fuller justification than minor clarifications.
When should a protocol paper be submitted?
As early as possible, ideally before recruitment is complete, so that peer review can still improve the study and the paper retains its transparency value. A protocol submitted after results are known cannot serve the purpose it exists for.