When One Paper Counts Many Times: A Bibliometric Study of Authorship Expansion, Publication-Credit Inflation, and Research Integrity Across Ten Medical Specialties, 2000–2025

Background Publication counts influence selection for medical training, academic promotion and administrative leadership positions even as the number of authors per paper rises. Awarding a full publication credit to every listed name can distort comparisons of research records and raises questions of fairness and accountability. I examined how 26 years of authorship expansion affected full versus equal-fraction counts for individual bibliographic author names. Methods Bibliometric census of PubMed-indexed research articles published 2000–2025 in 32 journals of ten specialties, with two PubMed-wide random samples. I modeled named authors per article (negative binomial models with journal-clustered standard errors; interrupted time series) and, for three 3-year windows, compared author names by full count, equal-fraction count and lead (first, last or sole) positions under four name-disambiguation rules. Results Among 177,486 research articles, mean authors rose from 6.4 to 14.2 (annual increase 3.5%, 95% CI 3.1–3.9), in all ten specialties and all 32 journals. At the author-name level (names with ≥ 2 initials), names with the same equal-fraction credit (0.9–1.1) listed 3–8 papers (10th–90th percentile) in 2000–2002 and 4–16 in 2023–2025 (increase in the 90th percentile 8 papers; 95% bootstrap CI 6–9.7), and the share of lead positions among the papers of the 100 names with the highest full count fell from 39% to 23% (decrease 15.1 percentage points; 95% CI 9.0–21.5). In 2023–2025, the top 100 names by full count shared 44–55 names with the top 100 by fractional count under the three stricter name rules (89 when all names were included). Of the 100 most prolific names, 35 probably merged different people. No clear discontinuity in author counts was observed after 2022. Conclusions Authorship expansion has made publication rankings of individual names strongly dependent on how credit is counted. Neither full nor equal-fraction counts measure actual contribution, and bibliographic records cannot identify honorary authorship. Nevertheless, using unadjusted publication volume to allocate competitive training, academic or administrative positions risks unfairly equating accumulated bylines with scientific achievement. Evaluation should prioritize the quality and originality of selected works and documented individual contributions.