Z.TEST function
Returns the onetailed Pvalue of a ztest.
For a given hypothesized population mean, x, Z.TEST returns the probability that the sample mean would be greater than the average of observations in the data set (array) — that is, the observed sample mean.
To see how Z.TEST can be used in a formula to compute a twotailed probability value, see the Remarks section below.
Syntax
Z.TEST(array,x,[sigma])
The Z.TEST function syntax has the following arguments:

Array Required. The array or range of data against which to test x.

x Required. The value to test.

Sigma Optional. The population (known) standard deviation. If omitted, the sample standard deviation is used.
Remarks

If array is empty, Z.TEST returns the #N/A error value.

Z.TEST is calculated as follows when sigma is not omitted:
Z.TEST(array,x,sigma) = 1 Norm.S.Dist((Average(array) x) / (sigma/√n),TRUE)
or when sigma is omitted:
Z.TEST(array,x) = 1 Norm.S.Dist((Average(array) x) / (STDEV(array)/√n),TRUE)
where x is the sample mean AVERAGE(array), and n is COUNT(array).

Z.TEST represents the probability that the sample mean would be greater than the observed value AVERAGE(array), when the underlying population mean is μ0. From the symmetry of the Normal distribution, if AVERAGE(array) < x, Z.TEST will return a value greater than 0.5.

The following Excel formula can be used to calculate the twotailed probability that the sample mean would be further from x (in either direction) than AVERAGE(array), when the underlying population mean is x:
=2 * MIN(Z.TEST(array,x,sigma), 1  Z.TEST(array,x,sigma)).
Example
The example may be easier to understand if you copy it to a blank worksheet.
How do I copy an example?

Select the example in this article.
Important Do not select the row or column headers.
Selecting an example from Help

Press CTRL+C.

In Excel, create a blank workbook or worksheet.

In the worksheet, select cell A1, and press CTRL+V.
Important For the example to work properly, you must paste it into cell A1 of the worksheet.

To switch between viewing the results and viewing the formulas that return the results, press CTRL+` (grave accent), or on the Formulas tab, in the Formula Auditing group, click the Show Formulas button.
After you copy the example to a blank worksheet, you can adapt it to suit your needs.

