Examples of how to use z-test functions
The z-test functions are used to find values associated with z-test statistical analysis for large data samples, usually greater than 30, and where the variance is known.
This section describes how to build visualizations using sample data to find the values of the z-test functions available in Qlik Sense. Please refer to the individual z-test chart function topics for descriptions of syntax and arguments.
Loading the sample data
The sample data used here is the same as that used in the t-test function examples. The sample data size would normally be considered too small for z-test analysis, but is sufficient for the purposes of illustrating the use of the different z-test functions in Qlik Sense.
Do the following:
- Create a new app with a new sheet.
-
In the data load editor, enter the following:
Table1: Crosstable (Type, Value) Load recno() as ID, * inline [ Observation|Comparison 35|2 40|27 12|38 15|31 21|1 14|19 46|1 10|34 28|3 48|1 16|2 30|3 32|2 48|1 31|2 22|1 12|3 39|29 19|37 25|2 ] (delimiter is '|');
In this load script, recno() is included because crosstable requires three arguments. So, recno() simply provides an extra argument, in this case an ID for each row. Without it, Comparison sample values would not be loaded.
- Click to load data.
Creating the z-test table
Do the following:
-
In the data load editor, click to go to app view, and then click the sheet you created above.
The sheet view is opened.
- Click Edit sheet to edit the sheet.
- From Charts add a table, and from Fields add Type as a dimension.
-
Add the following expressions to the table as measures
Label | Expression |
---|---|
ZTest Conf | ZTest_conf(Value) |
ZTest Dif | ZTest_dif(Value) |
ZTest Sig | ZTest_sig(Value) |
ZTest Sterr | ZTest_sterr(Value) |
ZTest Z | ZTest_z(Value) |
Result:
The resulting table for the z-test functions for the sample data will contain the following values:
Type | ZTest Conf | ZTest Dif | ZTest Sig | ZTest Sterr | ZTest Z |
---|---|---|---|---|---|
Comparison | 6.40 | 11.95 | 0.000123 | 3.27 | 3.66 |
Observation | 5.48 | 27.15 | 0.000000 | 2.80 | 9.71 |
Creating the z-testw table
The z-testw functions are for use when the input data series occurs in weighted two-column format. The expressions require a value for the argument weight.
The examples here use the value 2 throughout, but you could use an expression, which would define a value for weight for each observation.
Do the following:
-
In the data load editor, click to go to app view, and then click the sheet you created above.
The sheet view is opened.
- Click Edit sheet to edit the sheet.
- From Charts add a table, and from Fields add Type as a dimension.
-
Add the following expressions to the table as measures.
Example expressions Label Expression ZTestw Conf ZTestw_conf(2,Value) ZTestw Dif ZTestw_dif(2,Value) ZTestw Sig ZTestw_sig(2,Value) ZTestw Sterr ZTestw_sterr(2,Value) ZTestw Z ZTestw_z(2,Value) Use the same number formatting as in the z-test functions example.
Result:
The resulting table for the z-testw functions will contain the following values:
Type | ZTestw Conf | ZTestw Dif | ZTestw Sig | ZTestw Sterr | ZTestw Z |
---|---|---|---|---|---|
Comparison | 4.47 | 11.95 | 8.037185e-08 | 2.28 | 5.24 |
Observation | 3.83 | 27.15 | 0 | 1.95 | 13.91 |