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Confidence interval for a rate

Express result as 1:X


A rate is a ratio between a count and another measurement, for example the ratio of a number of events observed and the total number of person-years of observation.

Required input

  • Numerator: the observed number of events.
  • Denominator: for example the total person-years.
  • Option Express result as 1:X: when this option is selected the rate R will be displayed as 1:(1/R), e.g. the rate 10/200 equals 0.05 and can be represented as 1:20.


MedCalc displays:

  • The Poisson 95% Confidence Interval for the number counted (the Numerator).
  • The incidence rate.
  • The 95% Confidence Interval for the incidence rate.


  • Daly LE (1998) Confidence limits made easy: interval estimation using a substitution method. American Journal of Epidemiology 147:783-790.

How to cite this page

  • MedCalc Software Ltd. Confidence interval for a rate. (Version 22.030; accessed July 18, 2024)

See also