# ZTest\_conf - script and chart function

ZTest\_conf() returns the aggregated z value for a series of values.

If the function is used in the load script, the values are iterated over a number of records as defined by a group by clause.

If the function is used in a chart expression, the values are iterated over the chart dimensions.

Syntax:

ZTest\_conf(value[, sigma[, sig]])

Return data type: numeric

Arguments:

* value: The sample values to be evaluated. A population mean of 0 is assumed. If you want the test to be performed around another mean, subtract that mean from the sample values.
* sigma: If known, the standard deviation can be stated in sigma. If sigma is omitted the actual sample standard deviation will be used.
* sig: The two-tailed level of significance can be specified in sig. If omitted, sig is set to 0.025, resulting in a 95% confidence interval.

Limitations:

Text values, NULL values and missing values in the expression value will result in the function returning NULL.

Example:

` ZTest_conf(Value-TestValue)  `

## Learn more

* [Examples of how to use z-test functions](https://help.qlik.com/en-US/qlikview/September2026/Subsystems/Client/Content/QV_QlikView/ChartFunctions/StatisticalTestFunctions/ztest/ztest-example.htm)