Abstract
Equal-contribution authorship, in which two or more authors are designated as having contributed equally, is increasingly common in scientific publishing. Using ~480,000 tagged records extracted from over 45 million bibliographic XML files (PubMed and PMC, 2010-2024), we examine temporal trends, journal distributions, and geographic patterns. Results show a sharp rise after 2017, with both high-output mega-journals and smaller, discipline-specific journals contributing to the growth. Journal-level analysis indicates a median increase from ~19% in 2015 to over 30% in 2024. Geographically, China accounts for the largest share (40.8% of tagged cases), followed by the United States (15.2%) and Germany (5.2%). Normalizing to 2015 baselines, China shows a 13.1x increase by 2024, while even the slowest-growing countries more than tripled their rates. Collaboration networks highlight strong China-USA ties and identify mid-volume countries serving bridging roles. These findings document a broad shift toward shared first-author credit across journal sizes and regions within the biomedical literature. While this practice may improve equity in credit attribution, its rapid expansion merits continued monitoring and further analysis of domain-specific, institutional, and policy contexts.