A large-scale bibliometric analysis released in March 2026 puts numbers behind something authorship editors and research administrators have anecdotally noticed for years: the footnote marking two or more authors as having contributed equally to a paper is showing up far more often than it used to, and the increase has been sharp and recent rather than gradual.
What the study analyzed
The paper, “Trends in Equal-Contribution Authorship: A Large-Scale Bibliometric Analysis of Biomedical Literature” by Binbin Xu, was posted to arXiv in March 2026 (arXiv:2603.23569) and is also under review at Quantitative Science Studies, the MIT Press journal published on behalf of the International Society for Scientometrics and Informetrics. The analysis draws on approximately 480,000 tagged records from PubMed and PMC covering publication years 2010 through 2024, tracking how often articles carry an explicit equal-contribution designation, where in the byline those designations fall, which journals and countries drive the trend, and how the practice has moved over time.
This is a biomedical-literature study specifically — PubMed/PMC’s indexing scope — so its findings describe biomedicine and adjacent life-science fields rather than research publishing as a whole. That scope matters for how the numbers below should be read and cited.
The headline trend: a sharp rise after 2017
At the journal level, the median share of articles carrying an equal-contribution tag rose from roughly 19% in 2015 to more than 30% in 2024, with some journals now exceeding 50% of their published articles. The study identifies a sharp inflection after 2017, rather than a steady linear climb across the full 2010-2024 window — both high-output mega-journals and smaller, discipline-specific journals contributed to the acceleration.
That timing lines up with a period in which several major publishers and funders were actively formalizing contributorship reporting — CRediT (Contributor Roles Taxonomy) reached NISO recommended-practice status in 2022 after journals including PLOS, Cell Press, and others had already begun requiring structured contribution statements in the years before that — though the study itself is documenting the equal-contribution tag specifically, which predates and is conceptually distinct from CRediT’s twelve role categories. See CASRAI’s co-first authorship and equal-contribution guide for how the two concepts relate and how individual publishers implement the tag.
Where the growth is concentrated
The geographic breakdown is the study’s most striking finding. Measured by fractionalized contribution (each equally-contributing author counted proportionally rather than once per paper), China accounts for the largest share of equal-contribution designations at 40.8%, followed by the United States at 15.2% and Germany at 5.2%. China’s use of the designation grew roughly 13.1-fold between 2015 and 2024, and the paper reports that contributions from all countries in its analysis more than tripled over the same baseline period — meaning the practice is spreading broadly even where China’s absolute scale dominates the aggregate numbers.
The study also reports that equal-contribution designations cluster overwhelmingly near the first-author position in the byline rather than appearing in middle or final (senior-author) slots — consistent with co-first authorship’s original purpose of resolving credit disputes between researchers who did comparably foundational work, as opposed to senior/PI equal-contribution claims, which remain comparatively rare.
Why this matters for research administrators
A rising equal-contribution rate has practical downstream effects that research offices, tenure committees, and CRIS/RIMS administrators are increasingly having to account for:
- CV and dossier interpretation. A footnote asterisk carries real evaluative weight, but institutions vary widely in whether and how they factor equal-contribution status into tenure and promotion review. As the tag becomes more common, ad hoc handling becomes less defensible.
- Metadata and indexing. Equal-contribution status is inconsistently machine-readable across publishers — some encode it in JATS XML, most convey it only as free-text footnotes — which is part of why bibliometric studies like this one have to build custom extraction pipelines rather than querying a standard field.
- Author-order disputes. As the practice normalizes, research integrity offices are more likely to see disputes over who is included in an equal-contribution group, not just over first-author order generally — see CASRAI’s overview of authorship order conventions across disciplines.
- Cross-national policy variation. With China now the largest single source of equal-contribution designations by a wide margin, institutions evaluating international collaborators or co-authored grant applications should expect the practice to be more, not less, common going forward.
How this relates to other authorship-credit trends
This finding sits alongside other bibliometric signals CASRAI has covered recently: 2025 studies on the gender gap in corresponding and senior authorship found that women’s representation among first authors has grown faster than among senior/corresponding authors, and separate work has tracked a rise in single-author systematic reviews even as team size on primary research grows. Together, these point to authorship conventions that are actively in flux across several dimensions at once — team size, credit-sharing mechanisms, and who occupies which byline position — rather than a single uniform trend.
Reading the numbers carefully
A few scope notes are worth keeping in mind when citing this study. First, it covers biomedical literature indexed in PubMed/PMC only; equal-contribution practices in physics, mathematics, economics, or the humanities are not part of this dataset and may follow different patterns — CASRAI’s guide to authorship order conventions by discipline covers some of that cross-field variation. Second, “equal contribution” as tagged in these records reflects what publishers and authors chose to label, not an independent audit of actual work performed — the same caveat that applies to any self-reported contribution statement, including CRediT roles. Third, as of this writing the paper is a preprint under journal review rather than a final, copyedited publication; the topline figures above are unlikely to shift substantially through peer review, but exact percentages could still be refined before a final version of record.
Frequently asked questions
How many papers did the 2026 study analyze?
Approximately 480,000 tagged records from PubMed and PMC, covering publication years 2010 through 2024.
Is equal-contribution authorship the same as CRediT?
No. Equal-contribution (or co-first authorship) designations mark two or more authors as having contributed comparably to a paper, typically to the first-author position. CRediT (Contributor Roles Taxonomy) is a separate NISO-recognized framework that assigns each author one or more of twelve specific role categories (e.g., Data curation, Formal analysis, Writing – original draft). A paper can use both, either, or neither. See CASRAI’s co-first authorship and equal-contribution guide for the distinction.
Why did equal-contribution tagging rise sharply after 2017?
The study identifies the inflection but does not claim a single causal mechanism; it coincides with a period of broader movement toward formalized, granular authorship-credit reporting across major biomedical publishers, of which CRediT adoption is one visible part.
Does this study cover fields outside biomedicine?
No — the dataset is drawn entirely from PubMed and PMC, so the findings describe biomedical and closely related life-science literature. Trends in other disciplines are not part of this analysis.
