title: Sample size for post-marketing safety studies based on historical controls.
abstract: OBJECTIVE
  As part of a drug's entire life cycle, post-marketing studies are an important part in the identification of rare, serious adverse events. Recently, the US Food and Drug Administration (FDA) has begun to implement new post-marketing safety mandates as a consequence of increased emphasis on safety. The purpose of this research is to provide exact sample size formula for the proposed hybrid design, based on a two-group cohort study with incorporation of historical external data.
  
  
  METHODS
  Exact sample size formula based on the Poisson distribution is developed, because the detection of rare events is our outcome of interest. Performance of exact method is compared to its approximate large-sample theory counterpart.
  
  
  RESULTS
  The proposed hybrid design requires a smaller sample size compared to the standard, two-group prospective study design. In addition, the exact method reduces the number of subjects required in the treatment group by up to 30% compared to the approximate method for the study scenarios examined.
  
  
  CONCLUSIONS
  The proposed hybrid design satisfies the advantages and rationale of the two-group design with smaller sample sizes generally required.
authors.affiliation: Division of Biometrics VII, Office of Biostatistics, Center for Drug Evaluation and Research, US Food and Drug Administration, Silver Spring, MD 20993, USA. yutewu@yahoo.com
authors.forename: Yu-te
authors.initials: YT
authors.lastname: Wu
authors.forename: Robert W
authors.initials: RW
authors.lastname: Makuch
mesh_terms: D016907:Adverse Drug Reaction Reporting Systems; D015331:Cohort Studies; D016208:Databases, Factual; D064420:Drug-Related Side Effects and Adverse Reactions; D006801:Humans; D016012:Poisson Distribution; D011358:Product Surveillance, Postmarketing; D011446:Prospective Studies; D012107:Research Design; D018401:Sample Size; D016896:Treatment Outcome