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I knew a quite different definition of the Rule of three (1,2): “Rule of three states that consider a Bernoulli random variable with unknown probability “p”, if in N independent trials no events occur, a quick-and-ready approximation to the upper 95% confidence bound for “p” is 3/N”.
Andrea Messori, PharmD
Regional Health Service
1. Onbiostatistics website. Rule of three. Available at onbiostatistics.blogspot.it/2008/07/rule-of-three.html (accessed on 22 March 2018).
2. Ernst Eypasch E, Leferinga R, Kuma CK, Troidl H. Education And Debate. Probability of adverse events that have not yet occurred: a statistical reminder. BMJ 1995;311:619 doi: https://doi.org/10.1136/bmj.311.7005.619
No competing interests
22 March 2018
ESTAR, Regional Health Service, 50135 Firenze (Italy)