title: Citation classics in systematic reviews and meta-analyses: who wrote the top 100 most cited articles?
abstract: BACKGROUND
  Systematic reviews of the literature occupy the highest position in currently proposed hierarchies of evidence. The aims of this study were to assess whether citation classics exist in published systematic review and meta-analysis (SRM), examine the characteristics of the most frequently cited SRM articles, and evaluate the contribution of different world regions.
  
  
  METHODS
  The 100 most cited SRM were identified in October 2012 using the Science Citation Index database of the Institute for Scientific Information. Data were extracted by one author. Spearman's correlation was used to assess the association between years since publication, numbers of authors, article length, journal impact factor, and average citations per year.
  
  
  RESULTS
  Among the 100 citation classics, published between 1977 and 2008, the most cited article received 7308 citations and the least-cited 675 citations. The average citations per year ranged from 27.8 to 401.6. First authors from the USA produced the highest number of citation classics (n=46), followed by the UK (n=28) and Canada (n=15). The 100 articles were published in 42 journals led by the Journal of the American Medical Association (n=18), followed by the British Medical Journal (n=14) and The Lancet (n=13). There was a statistically significant positive correlation between number of authors (Spearman's rho=0.320, p=0.001), journal impact factor (rho=0.240, p=0.016) and average citations per year. There was a statistically significant negative correlation between average citations per year and year since publication (rho = -0.636, p=0.0001). The most cited papers identified seminal contributions and originators of landmark methodological aspects of SRM and reflect major advances in the management of and predisposing factors for chronic diseases.
  
  
  CONCLUSIONS
  Since the late 1970s, the USA, UK, and Canada have taken leadership in the production of citation classic papers. No first author from low or middle-income countries (LMIC) led one of the most cited 100 SRM.
authors.affiliation: Warwick Centre for Applied Health Research and Delivery (WCAHRD), Division of Health Sciences, Warwick Medical School, the University of Warwick, Coventry, United Kingdom ; International Health Group, Liverpool School of Tropical Medicine, Liverpool, United Kingdom ; Centre for Evidence-Based Health Care, Faculty of Medicine and Health Sciences, Stellenbosch University, Tygerberg, South Africa.
authors.forename: Olalekan A
authors.initials: OA
authors.lastname: Uthman
authors.forename: Charles I
authors.initials: CI
authors.lastname: Okwundu
authors.forename: Charles S
authors.initials: CS
authors.lastname: Wiysonge
authors.forename: Taryn
authors.initials: T
authors.lastname: Young
authors.forename: Aileen
authors.initials: A
authors.lastname: Clarke
mesh_terms: D001319:Authorship; D005843:Geography; D006801:Humans; D055811:Journal Impact Factor; D015201:Meta-Analysis as Topic; D010506:Periodicals as Topic; D011642:Publications; D012196:Review Literature as Topic