Create a data set for the grouping panel that contains the subset, and:
In the Custom Data Dimensions section of the
Data Set Properties dialog box, add a custom
data dimension for the subset key item.
The name of the custom data
dimension becomes the name of the subset key item in the data
mappings and in the Clintrial panel. This name must not be the same
as the RefName or alias of any data series in the data set.
In the Custom Dimension Labels - Select Codelist
dialog box, select or create a codelist that has a codelist item label
for each value that the subset key item can have.