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Trends in Equal-Contribution Authorship: A Large-Scale Bibliometric Analysis of Biomedical Literature

Binbin Xu

Abstract

Equal-contribution authorship, in which two or more authors are designated as having contributed equally, is increasingly common in scientific publishing. Using approximately 480,000 tagged records from PubMed and PMC (2010-2024), we examine temporal trends, journal-level patterns, geographic distributions, and byline positions of equal-contributing authors. 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 in the share of tagged articles from about 19% in 2015 to over 30% in 2024, with some journals exceeding 50%. Geographically, China accounts for the largest share (40.8% of fractionalized contributions), 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 levels. Analysis of normalized byline positions shows that equal-contribution designations are concentrated near the first-author position, with fewer cases in middle or last positions. These findings document a broad shift toward shared first-author credit across journal sizes and regions within the biomedical literature and suggest that journals and evaluators may need to rely more on transparent contributorship information and to monitor the use of such labels over time.

Trends in Equal-Contribution Authorship: A Large-Scale Bibliometric Analysis of Biomedical Literature

Abstract

Equal-contribution authorship, in which two or more authors are designated as having contributed equally, is increasingly common in scientific publishing. Using approximately 480,000 tagged records from PubMed and PMC (2010-2024), we examine temporal trends, journal-level patterns, geographic distributions, and byline positions of equal-contributing authors. 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 in the share of tagged articles from about 19% in 2015 to over 30% in 2024, with some journals exceeding 50%. Geographically, China accounts for the largest share (40.8% of fractionalized contributions), 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 levels. Analysis of normalized byline positions shows that equal-contribution designations are concentrated near the first-author position, with fewer cases in middle or last positions. These findings document a broad shift toward shared first-author credit across journal sizes and regions within the biomedical literature and suggest that journals and evaluators may need to rely more on transparent contributorship information and to monitor the use of such labels over time.
Paper Structure (7 sections, 2 equations, 7 figures, 1 table)

This paper contains 7 sections, 2 equations, 7 figures, 1 table.

Table of Contents

  1. Introduction
  2. Data
  3. Results
  4. Trends in Equal-Contribution Authorship
  5. Journal-level Prevalence Patterns
  6. Geographic Pattern
  7. Discussion and Conclusion

Figures (7)

  • Figure 1: Data-flow diagram showing the filtering, matching, and date-restriction steps applied to PubMed and PubMed Central (PMC) records to produce the final analysis set for 2010-2024.
  • Figure 2: Trends in the use of equal-contribution authorship in scientific publications. Left: Annual count of publications explicitly labeling at least two authors as having contributed equally, showing a strong upward trend from 2010 to 2024. Right: Distribution of the top 100 journals ranked by proportion of equal-contribution articles (2010-2024).
  • Figure 3: Distribution of byline positions among equal-contributing authors. The normalized position is defined as $(p-1)/(\texttt{num\_authors}-1)$, so that 0 corresponds to the first author and 1 to the last author. Left: absolute counts of equal-contributing authors by normalized position. Right: the same distribution expressed as percentages.
  • Figure 4: Changes in equal-contribution authorship over time at the journal level. Heatmap of 143 journals with a median proportion of equal-contribution articles $\geq 20\%$ in the last five years (2020-2024); colors indicate yearly percentages. These values are descriptive only and should not be interpreted as evaluative of editorial policies or journal quality.
  • Figure 5: Relationship between annual journal output and the proportion of equal-contribution authorship (Left), and yearly distribution of equal-contribution ratios across all journals (Right). The scatter plot shows individual journal-year points, color-coded by year; the boxplots summarize the spread and median ratio for 2015-2024.
  • ...and 2 more figures