# Z-test

A **z-test** is similar to a *t*-test. In both cases, the central tendency of a normally distributed sample is compared with either a fixed value or the value of another group.

*z*-scores indicate the difference between the observed distribution and the comparison in standard deviation units. *z*-scores derive from the properties of a normal distribution (e.g., 95% of scores will be less than a standardised *z*-score of 1.96).