Statistics & probability
Wilson proportion interval
Calculate a bounded confidence interval for a count out of a sample.
A clear answer. Here’s how.
Uses the two-sided Wilson score interval with a numerically computed standard-normal critical value. Successes must be 0–sample size. Assumes independent Bernoulli observations with a common probability and an appropriate sample design. A confidence level describes repeated-sampling coverage, not a probability assigned to this fixed population parameter.
See a worked example
Worked example
A fixed demonstration, separate from the values you enter above.
- Success count
- 26
- Sample size
- 200
- Two-sided confidence level (%)
- 95
Example result
- Observed proportion
- 0.13
- Wilson lower bound
- 0.0902820227967
- Wilson upper bound
- 0.183663518722
- Confidence level
- 95%