# ZTEST

Returns the result of a z-test.

### Syntax:

ZTEST(data, μ, σ)

data is a range or array containing a random sample from a population (population assumed to have a normal distribution).
μ is the (known) mean of the population.
σ is the (known) standard deviation of the population. If omitted, it is estimated from the sample data by STDEV(data).
ZTEST calculates the z statistic:

where m is the sample mean and n the number in the sample. When the mean and standard deviation of the population are known, the z statistic forms a standard normal distribution - that is, a normal distribution with mean=0 and standard deviation=1.
ZTEST returns the one-sided cumulative probability - the area under the standard normal curve to the right of the z value (shaded blue here):

### Example:

ZTEST(A2:A20, 9, 2)
returns the result of a z-test on a sample A2:A20 drawn from a population with known mean 9 and known standard deviation 2.