Pre-publication peer review has been part of science for a long time. Philosophical Transactions, the first peer-reviewed journal, published its first paper in 1665 but peer review may be even older still. There are records of physicians in the Arab world reviewing the effectiveness of each other’s treatments as early as the 9th century.

Peer review is a critical part of the modern scientific process. For science to progress, research methods and findings need to be closely examined and verified, and from them a decision on the best direction for future research is made. After a study has gone through peer review and is accepted for publication, scientists and the public can be confident that the study has met certain standards, and that the results can be trusted.

After an editor receives a manuscript, their first step is to check that the manuscript meets the journal’s rules for content and format. If it does, then the editor moves to the next step, which is peer review. The editor will send the manuscript to two or more experts in the field to get their opinion. The experts – called peer reviewers – will then prepare a report that assesses the manuscript, and return it to the editor. After reading the peer reviewer's report, the editor will decide to do one of three things: reject the manuscript, accept the manuscript, or ask the authors to revise and resubmit the manuscript after responding to the peer reviewers’ feedback. If the authors resubmit the manuscript, editors will sometimes ask the same peer reviewers to look over the manuscript again to see if their concerns have been addressed. This is called re-review.

Some of the problems that peer reviewers may find in a manuscript include errors in the study’s methods or analysis that raise questions about the findings, or sections that need clearer explanations so that the manuscript is easily understood. From a journal editor’s point of view, comments on the importance and novelty of a manuscript, and if it will interest the journal’s audience, are particularly useful in helping them to decide which manuscripts to publish.

Different types of peer review

Although the basis of peer review is the same across all journals, experts providing comments on a manuscript submitted to the journal, there are different types in existence. The most common of these are:

  • Closed peer review – where the reviewers are aware of the authors’ identities but the authors’ are never informed of the reviewers’ identities.
  • Double-blind peer review – where neither author nor reviewer is aware of each other’s identities.
  • Open peer review – where authors and reviewers are aware of each other’s identity. In some journals with open peer review the reviewers’ reports are published alongside the article.

The type of peer review used by a journal should be clearly stated in the invitation to review letter you receive and policy pages on the journal website. If, after checking the journal website, you are unsure of the type of peer review used or would like clarification on the journal’s policy you should contact the journal’s editors.