title: Inflated numbers of authors over time have not been just due to increasing research complexity.
abstract: OBJECTIVE
  To examine trends in and determinants of the number of authors in clinical studies.
  
  
  METHODS
  We analyzed determinants of the number of authors in 633 articles of randomized trials and 313 articles of nonrandomized studies included in large meta-analyses (seven and six topics, respectively). Analyses were adjusted for topic. We also evaluated 310 randomly sampled case reports that had an abstract and described a single case.
  
  
  RESULTS
  After adjusting for topic and other determinants, for both randomized trials and nonrandomized studies, the number of authors increased by 0.8 per decade (P<0.001). Topic was a strong determinant of the number of authors; other independent factors included journal impact factor, multinational authorship, and (for randomized trials) article length and sample size. Trials from South Europe (+1.1 authors) and North America (+0.9) and nonrandomized studies from South Europe (+1.8) had more authors than studies from North Europe (P<0.001). For case reports, only geographic location and article length were significantly related with author numbers.
  
  
  CONCLUSIONS
  The number of authors in articles of randomized and nonrandomized studies has increased over time, even after adjusting for the topic, size, and visibility of a study. The academic coinage of authorship may be suffering from inflation.
authors.affiliation: Evidence-Based Medicine and Clinical Trials Unit, Department of Hygiene and Epidemiology, University of Ioannina School of Medicine, Ioannina, Greece.
authors.forename: Stefania I
authors.initials: SI
authors.lastname: Papatheodorou
authors.forename: Thomas A
authors.initials: TA
authors.lastname: Trikalinos
authors.forename: John P A
authors.initials: JP
authors.lastname: Ioannidis
mesh_terms: D001319:Authorship; D015706:Bibliometrics; D035843:Biomedical Research / Q000639:trends*; D006801:Humans; D008499:Medical Records / Q000706:statistics & numerical data; D010506:Periodicals as Topic / Q000706:statistics & numerical data / Q000639:trends; D011643:Publishing / Q000706:statistics & numerical data / Q000639:trends; D016032:Randomized Controlled Trials as Topic / Q000706:statistics & numerical data / Q000639:trends