{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,1]],"date-time":"2026-10-01T18:03:01Z","timestamp":1790877781131,"version":"4.1.0"},"reference-count":30,"publisher":"Public Library of Science (PLoS)","issue":"10","license":[{"start":{"date-parts":[[2026,10,1]],"date-time":"2026-10-01T00:00:00Z","timestamp":1790812800000},"content-version":"vor","delay-in-days":0,"URL":"http:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":["www.plosone.org"],"crossmark-restriction":false},"short-container-title":["PLoS One"],"abstract":"<jats:p>The relative age effect (RAE) \u2014 the overrepresentation of players born early in the selection year \u2014 is one of the most robust findings in sports science, yet how much it varies across countries and over time remains surprisingly underexplored. Drawing on birth-date data for 49,578 male professional footballers across 44 national systems and five birth cohorts (1985\u20132009), this study describes three patterns that have not previously been examined together. RAE magnitude varies enormously across national football systems, ranging from close to zero to birth-quarter gaps exceeding 40 percentage points. It has also increased across successive birth cohorts: players born in 2005\u20132009 show birth-quarter imbalances roughly 9 percentage points wider than those born in 1985\u20131989. Common macro-level indicators \u2014 national footballing strength, gross domestic product (GDP) per capita, and population \u2014 show at most weak and inconsistent associations with cross-national differences in RAE and do not account for the historical increase once country and cohort are held fixed. Together, these findings provide a comparative benchmark for understanding cross-national and historical variation in relative age effects.<\/jats:p>","DOI":"10.1371\/journal.pone.0354928","type":"journal-article","created":{"date-parts":[[2026,10,1]],"date-time":"2026-10-01T17:25:46Z","timestamp":1790875546000},"page":"e0354928","update-policy":"https:\/\/doi.org\/10.1371\/journal.pone.corrections_policy","source":"Crossref","is-referenced-by-count":0,"title":["Cross-national and historical variation in relative age effects in professional football"],"prefix":"10.1371","volume":"21","author":[{"ORCID":"https:\/\/orcid.org\/0000-0001-6751-5429","authenticated-orcid":true,"given":"Thomas Ulrich","family":"Grund","sequence":"first","affiliation":[{"name":"Institute of Sociology, RWTH Aachen University","place":["Aachen, Germany"]}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"340","published-online":{"date-parts":[[2026,10,1]]},"reference":[{"issue":"1","key":"pone.0354928.ref001","first-page":"23","article-title":"Hockey success and birthdate: The relative age effect","volume":"51","author":"RH Barnsley","year":"1985","journal-title":"CAHPER J"},{"issue":"1","key":"pone.0354928.ref002","doi-asserted-by":"crossref","first-page":"77","DOI":"10.1177\/101269029202700105","article-title":"Family planning: Football style. 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