# ZTestw\_dif Script and chart function

ZTestw\_dif() returns the aggregated z-test mean difference for a series of values.

This function applies to z-tests where the input data series is given in weighted two-column format.

If the function is used in the data 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:

ZTestw\_dif ( weight, value [, sigma])

Return data type: numeric

Arguments:

Arguments

| Argument | Description |
| --- | --- |
| value | The values should be returned by value. A sample mean of 0 is assumed. If you want the test to be performed around another mean, subtract that value from the sample values. |
| weight | Each sample value in<br>value can be counted one or more<br>times according to a corresponding weight value in weight. |
| sigma | If known, the standard deviation can be stated in sigma. If sigma is omitted the actual sample standard deviation will be used. |

Limitations:

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

Example:

`ZTestw_dif( 
 Weight, Value-TestValue)`

## Learn more

* [Examples of how to use z-test functions](https://help.qlik.com/en-US/cloud-services/Subsystems/Hub/Content/Sense_Hub/ChartFunctions/StatisticalTestFunctions/ztest/ztest-example.htm)