Freedom Calculator

Confidence of population freedom for multiple time periods

Input Values

Submit Data

Note: this now requires inclusion of a header row in the data
Initial prior confidence of freedom
Data: Download example data

Note: This page now accepts data where either a comma (,) or point (.) is used as the decimal separator.

Calculate the confidence of country or area freedom from disease/infection

  • over multiple time periods
  • when the sensitivity of the surveillance system in each time period is known (or can be estimated)
  • when the likelihood of introduction of disease (or of disease exceeding the design prevalence) in each time period is known (or can be estimated)
  • when the prior confidence of freedom can be estimated

Data Format

To submit data, enter it into three columns of a spreadsheet, copy it and paste it into the text box below. The format requirements are:

  • three columns only
  • include a header of column names (Note: this has changed from previously when a header row was not required)
  • first column: Period (a number or text label to describe each period, eg 2001, 2003...)
  • second column: System sensitivity (between 0 and 1 - i.e. not as a percentage)
  • third column: Risk of introduction of disease during each time period (between 0 and 1)


Outputs are a table and plot of the following values:

  • System sensitivity for each time period (input);
  • Posterior confidence of freedom at the end of each time period;
  • Probability of introduction during each time period (input);
  • Prior probability of freedom for each time period (after adjusting for possible introduction during the period); and
  • Equilibrium confidence of freedom - the stable maximum (or minimum) value for confidence of freedom for given SSe and PIntro for each time period (see Watkins, et al., 2009. An evaluation of the sensitivity of acute flaccid paralysis surveillance for poliovirus infection in Australia. BMC Infectious Diseases, 9, 162).

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This site was created by Ausvet with funding from a range of sources.
It provides a range of epidemiological tools for the use of researchers and epidemiologists, particularly in animal health.
Please send any comments, questions or suggestions to Evan Sergeant
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