title: Clinical "case series": a concept analysis.
abstract: OBJECTIVE
  To analyze the concept of "case series" in the medical literature compared with case reports.
  
  
  METHODS
  A PubMed search for articles published during 2009 which had "case series" in their title was performed. A total number of 621 articles were retrieved. 586 papers were included in the analysis and 35 were excluded (18 were commentary letters, 5 were not in English, and twelve could not be retrieved by our Library). The number of patients and category of these articles were analyzed.
  
  
  RESULTS
  The median (range) of the number of cases of articles having "case series" in their title was 7 (1-6432) cases. 186/ 586 articles had less than 5 cases (31.7%, 95% CI (28.3-35.1%)). The median (range) of the number of cases of articles having "case report" as their publication type was 4 (1-178) cases. Out of the 219 articles categorized as case reports 114 (52.1%, 95% CI (45.6-58.6%)) had less than five cases.
  
  
  CONCLUSIONS
  The concept of "case series" is not well defined in the literature and does not reflect a specific research design. We suggest that a case series should have more than four patients while four paitents or less should be reported individually as case reports.
authors.affiliation: Trauma Research Group, Faculty of Medicine and Health Sciences, UAE University, Al-Ain, UAE. fabuzidan@uaeu.ac.ae
authors.forename: F M
authors.initials: FM
authors.lastname: Abu-Zidan
authors.forename: A K
authors.initials: AK
authors.lastname: Abbas
authors.forename: A F
authors.initials: AF
authors.lastname: Hefny
mesh_terms: D006801:Humans; D008297:Male; D011642:Publications; D011643:Publishing; D012107:Research Design
keywords: Case report; case series; concept analysis; research design