Calculate confidence limits for a sample proportion

Input Values


This utility calculates confidence limits for a population proportion for a specified level of confidence.

Inputs are the sample size and number of positive results, the desired level of confidence in the estimate and the number of decimal places required in the answer.

The program outputs the estimated proportion plus upper and lower limits of the specified confidence interval, using 5 alternative calculation methods decribed and discussed in Brown, LD, Cat, TT and DasGupta, A (2001). Interval Estimation for a proportion. Statistical Science 16:101-133:

  1. Asymptotic (Wald) method based on a normal approximation,
  2. Binomial (Clopper-Pearson) 'exact' method based on the beta distribution,
  3. 'Wilson' Score interval,
  4. 'Agresti-Coull' (adjusted Wald) interval and
  5. 'Jeffreys' interval.

The Wald interval often has inadequate coverage, particularly for small n and values of p close to 0 or 1. Conversely, the Clopper-Pearson Exact method is very conservative and tends to produce wider intervals than necessary. Brown et al. recommends the Wilson or Jeffreys methods for small n and Agresti-Coull, Wilson, or Jeffreys, for larger n as providing more reliable coverage than the alternatives. Also note that the point estimate for the Agresti-Coull method is slightly larger than for other methods because of the way this interval is calculated.

Sample size :
Number positive :
Confidence level:
Confidence interval method:
Decimal places in answer :

There is no result available for this test

If this is surprising please contact Ausvet (Email Evan) and advise what test you were trying.

Please copy the url from the address bar (also shown below) and include it in the email as it will allow us to work on the problem using the same parameters that you have been using.

_POST variables



  Home  |   About this site  |   Glossary   |   References   |   Links   |  237 recent calculations

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
© 2018 Ausvet