title: Case series and descriptive cohort studies in neurosurgery: the confusion and solution.
abstract: BACKGROUND
  Case series (CS) are well-known designs in contemporary use in neurosurgery but are sometimes used in contexts that are incompatible with their true meaning as defined by epidemiologists. This inconsistent, inappropriate and incorrect use, and mislabeling impairs the appropriate indexing and sorting of evidence.
  
  
  METHODS
  Using PubMed, we systematically identified published articles that had "case series" in the "title" in 15 top-ranked neurosurgical journals from January 2008 to December 2012. The abstracts and/or full articles were scanned to identify those with descriptions of the principal method as being "case series" and then classified as "true case series" or "non-case series" by two independent investigators with 100 % inter-rater agreement.
  
  
  RESULTS
  Sixty-four articles had the label "case series" in their "titles." Based on the definition of "case series" and our appraisal of the articles using Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) guidelines, 18 articles (28.13 %) were true case series, while 46 (71.87 %) were mislabeled. Thirty-five articles (54.69 %) mistook retrospective (descriptive) cohorts for CS. CS are descriptive with an outcome-based sampling, while "descriptive cohorts" have an exposure-based sampling of patients, followed over time to assess outcome(s). A comparison group is not a defining feature of a cohort study and distinguishes descriptive from analytic cohorts.
  
  
  CONCLUSIONS
  A distinction between a case report, case series, and descriptive cohorts is absolutely necessary to enable the appropriate indexing, sorting, and application of evidence. Researchers need better training in methods and terminology, and editors and reviewers should scrutinize more carefully manuscripts claiming to be "case series" studies.
authors.affiliation: Department of Neurosurgery, Ain Shams University, Cairo, Egypt, ignatiusesene@yahoo.co.uk.
authors.forename: Ignatius N
authors.initials: IN
authors.lastname: Esene
authors.forename: Julius
authors.initials: J
authors.lastname: Ngu
authors.forename: Mohamed
authors.initials: M
authors.lastname: El Zoghby
authors.forename: Ihsan
authors.initials: I
authors.lastname: Solaroglu
authors.forename: Anna M
authors.initials: AM
authors.lastname: Sikod
authors.forename: Ali
authors.initials: A
authors.lastname: Kotb
authors.forename: Gilbert
authors.initials: G
authors.lastname: Dechambenoit
authors.forename: Hossam
authors.initials: H
authors.lastname: El Husseiny
mesh_terms: D015331:Cohort Studies; D006801:Humans; D009422:Nervous System Diseases / Q000601:surgery*; D009493:Neurosurgery / Q000379:methods*; D039781:PubMed / Q000706:statistics & numerical data