WorksheetFunction.ZTest Method

Syntax

expression.ZTest(Arg1, Arg2, Arg3)

expression A variable that represents a WorksheetFunction object.

Parameters

Name	Required/Optional	Data Type	Description
Arg1	Required	Variant	Array is the array or range of data against which to test the hypothesized population mean.
Arg2	Required	Double	The value to test.
Arg3	Optional	Variant	Sigma - the population (known) standard deviation. If omitted, the sample standard deviation is used.

Return Value
Double

Remarks

If array is empty, ZTEST returns the #N/A error value.
ZTEST is calculated as follows when sigma is not omitted:

or when sigma is omitted:

where x is the sample mean AVERAGE(array); s is the sample standard deviation STDEV(array); and n is the number of observations in the sample COUNT(array).
ZTEST 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) < μ₀, ZTEST will return a value greater than 0.5.
The following Excel formula can be used to calculate the two-tailed probability that the sample mean would be further from μ₀ (in either direction) than AVERAGE(array), when the underlying population mean is μ₀:
=2 * MIN(ZTEST(array,μ₀,sigma), 1 - ZTEST(array,μ₀,sigma)).

Returns the one-tailed probability-value of a z-test. For a given hypothesized population mean, ZTEST 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.