WorksheetFunction.ZTest Method

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Excel Developer Reference

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.

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:

    Formula

    or when sigma is omitted:

    Formula

    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)).

See Also