A Look at the Rule of Three

B. D. Jovanovic, P. S. Levy

Research output: Contribution to journalArticlepeer-review

112 Scopus citations


The Rule of Three states that 3/n is an upper 95% confidence bound for binomial probability p when in n independent trials no events occur. We discuss the derivation of this rule, its validity in small samples, and propose some alternatives. The material may serve well as a thought-provoking introduction to a clinical trials, statistical consulting, or a categorical data class, and is interesting on its own merit.

Original languageEnglish (US)
Pages (from-to)137-139
Number of pages3
JournalAmerican Statistician
Issue number2
StatePublished - May 1997


  • Binomial probability
  • Clinical research
  • Safety

ASJC Scopus subject areas

  • Statistics and Probability
  • Mathematics(all)
  • Statistics, Probability and Uncertainty


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