Research brief · 2026-09-09
Preprints, Peer Review, and What the Difference Is Worth
A preprint is a complete manuscript posted to a public server such as medRxiv, bioRxiv or Research Square, usually when it is submitted to a journal or sometimes before. Nothing in that step involves an outside expert checking the statistics, questioning the design, or catching an error in interpretation. That is what peer review adds. The journal version, if it appears at all, has typically been revised in response. The preprint is whatever the authors submitted.
A 2021 study in PeerJ by Anazco and colleagues tracked 5,061 COVID-19 preprints posted between January and May 2020. Only 288, or 5.7 percent, had been published in a peer-reviewed journal by the time they checked. The observation window matters, though. A 2023 study in Clinical Orthopaedics and Related Research by Rizk and colleagues tracked 1,471 orthopaedic preprints from 2014 through 2021 and found 52 percent were matched to a peer-reviewed publication over that longer span.
A sharper question is whether review changes anything. A 2023 study in the Journal of Intensive Care Medicine by Morin and colleagues compared 21 preprints on COVID-19 critical-care therapies to their published versions. Only one changed its primary outcome, so the headline claim mostly held. But seven, 33 percent, changed the size of the primary effect. Five changed the significance of a secondary outcome. And four, 19 percent, nearly one in five, changed the study's stated conclusion.
Together these describe a bounded role for preprints. They get findings into view fast, which mattered during a pandemic. But many never complete the trip within a given window, and among those that do, roughly one in five sees a real change to what it claims. Both bioRxiv and medRxiv show a published-in link once the reviewed version exists. What these studies do not tell you is why specific preprints never get published, whether the rate applies to slower fields like peptide research, or whether the reviewed version was actually closer to the truth. Sources are listed below.
Sources
- Anazco D et al., Publication rate and citation counts for preprints released during the COVID-19 pandemic (n=5,061 preprints)
- PeerJ, 2021
- Rizk AA et al., Characterization and reach of orthopaedic research posted to preprint servers (n=1,471 preprints)
- Clinical Orthopaedics and Related Research, 2023
- Morin C et al., Comparison of COVID-19 preprint and peer-reviewed versions of studies on therapies for critically ill patients (n=21 pairs)
- Journal of Intensive Care Medicine, 2023
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