title: Case-only designs in pharmacoepidemiology: a systematic review.
abstract: BACKGROUND
  Case-only designs have been used since late 1980's. In these, as opposed to case-control or cohort studies for instance, only cases are required and are self-controlled, eliminating selection biases and confounding related to control subjects, and time-invariant characteristics. The objectives of this systematic review were to analyze how the two main case-only designs - case-crossover (CC) and self-controlled case series (SCCS) - have been applied and reported in pharmacoepidemiology literature, in terms of applicability assumptions and specificities of these designs.
  
  
  RESULTS
  We systematically selected all reports in this field involving case-only designs from MEDLINE and EMBASE up to September 15, 2010. Data were extracted using a standardized form. The analysis included 93 reports 50 (54%) of CC and 45 (48%) SCCS, 2 reports combined both designs. In 12 (24%) CC and 18 (40%) SCCS articles, all applicable validity assumptions of the designs were fulfilled, respectively. Fifty (54%) articles (15 CC (30%) and 35 (78%) SCCS) adequately addressed the specificities of the case-only analyses in the way they reported results.
  
  
  CONCLUSIONS
  Our systematic review underlines that implementation of CC and SCCS designs needs to be more rigorous with regard to validity assumptions, as well as improvement in results reporting.
authors.affiliation: Univ Paris Diderot, Sorbonne Paris Cité, UMR-S 738; INSERM, UMR-S 738, Paris, France.
authors.forename: Sandra
authors.initials: S
authors.lastname: Nordmann
authors.forename: Lucie
authors.initials: L
authors.lastname: Biard
authors.forename: Philippe
authors.initials: P
authors.lastname: Ravaud
authors.forename: Marina
authors.initials: M
authors.lastname: Esposito-Farèse
authors.forename: Florence
authors.initials: F
authors.lastname: Tubach
mesh_terms: D018592:Cross-Over Studies; D064420:Drug-Related Side Effects and Adverse Reactions; D015340:Epidemiologic Research Design; D016239:MEDLINE; D017891:Pharmacoepidemiology / Q000379:methods* / Q000592:standards; D012107:Research Design