# Free statistical calculators

## Test for one proportion

## Computational notes

### P-value

The significance level, or P-value, is calculated using a general z-test (Altman, 1991):

where *p* is the observed proportion; *p*_{exp} is the Null hypothesis (or expected) proportion; and *se*(*p*) is the standard error of the expected proportion:

The P-value is the area of the normal distribution that falls outside ±*z* (see Values of the Normal distribution table).

### Confidence interval

MedCalc calculates the "exact" Clopper-Pearson confidence interval for the observed proportion.

## Literature

- Altman DG (1991) Practical statistics for medical research. London: Chapman and Hall.

## External links

- Binomial proportion confidence interval on Wikipedia.