# Statistics/Testing Data/z-testsprop

*z* test statistic: one proportion[edit]

A test statistic that represents the difference between the hypothesized proportion and the observed proportion is used when the binomial parameter *p* is being tested through the use of a hypothesis-testing procedure. This value is then divided by the standard error. When *n* is significantly large (*n* > 20, *np* > 5, and *nq* > 5), the test assumptions have been satisfied, and the null hypothesis is true, then we assume that the test statistic is normally distributed.