Check this box to subset the available variables to only include those variables that are domain keys. If the option is unchecked, the report uses the cross-classification of xxCAT, xxSCAT, xxLOC, xxMETHOD, xxPOS, xxSPEC, and xxTPT for creating by groups for all variables that are available (as it had in the past).
For example, suppose a sponsor collects blood pressure measurements and records the xxLOC to be either RIGHT or LEFT to indicate the arm that was selected. This is really just additional information, and not really part of a design that needs to be considered and would not be captured when the box is checked. Contrast this with ocular studies where xxLOC would be recorded as OD to indicate the right eye or OS to indicate the left. Here, xxLOC would need to be captured as a domain KEY since it would be the only thing that distinguishes the row between a left and right eye. Similarly, for lab work, where xxSPEC could be BLOOD or URINE with the same labtestcd is computed. This is part of the design, and would need to be considered a KEY.
Note: When building the BY variables lists, if this option is checked, there is an additional step to see if the variable is a KEY. If it is, then it is added to the list.
