title: Citation analysis of orthopaedic literature; 18 major orthopaedic journals compared for Impact Factor and SCImago.
abstract: BACKGROUND
  One of the disadvantages of the Impact Factor (IF) is self-citation. The SCImago Journal Rank (SJR) indicator excludes self-citations and considers the quality, rather than absolute numbers, of citations of a journal by other journals. The present study re-evaluated the influence of self-citation on the 2007 IF for 18 major orthopaedic journals and investigated the difference in ranking between IF and SJR.
  
  
  METHODS
  The journals were analysed for self-citation both overall and divided into a general group (n = 8) and a specialized group (n = 10). Self-cited and self-citing rates, as well as citation densities and IFs corrected for self-citation (cIF), were calculated. The rankings of the 18 journals by IF and by SJR were compared and the absolute difference between these rankings (DeltaR) was determined.
  
  
  RESULTS
  Specialized journals had higher self-citing rates (p = 0.01, Deltamedian = 9.50, 95%CI -19.42 to 0.42), higher self-cited rates (p = 0.0004, Deltamedian = -10.50, 95%CI -15.28 to -5.72) and greater differences between IF and cIF (p = 0.003, Deltamedian = 3.50, 95%CI -6.1 to 13.1). There was no significant correlation between self-citing rate and IF for both groups (general: r = 0.46, p = 0.27; specialized: r = 0.21, p = 0.56). When the difference in ranking between IF and SJR was compared between both groups, sub-specialist journals were ranked lower compared to their general counterparts (DeltaR: p = 0.006, Deltamedian = 2.0, 95%CI -0.39 to 4.39).
  
  
  CONCLUSIONS
  Citation analysis shows that specialized orthopaedic journals have specific self-citation tendencies. The correlation between self-cited rate and IF in our sample was large but, due to small sample size, not significant. The SJR excludes self-citations in its calculation and therefore enhances the underestimation in ranking of specialized journals.
authors.forename: Michiel
authors.initials: M
authors.lastname: Siebelt
authors.forename: Teun
authors.initials: T
authors.lastname: Siebelt
authors.forename: Peter
authors.initials: P
authors.lastname: Pilot
authors.forename: Rolf M
authors.initials: RM
authors.lastname: Bloem
authors.forename: Mohit
authors.initials: M
authors.lastname: Bhandari
authors.forename: Rudolf W
authors.initials: RW
authors.lastname: Poolman
mesh_terms: D003627:Data Interpretation, Statistical; D006801:Humans; D055811:Journal Impact Factor; D009985:Orthopedics / Q000706:statistics & numerical data* / Q000639:trends*; D017712:Peer Review, Research / Q000592:standards / Q000639:trends; D010506:Periodicals as Topic / Q000706:statistics & numerical data* / Q000639:trends*