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ItemGroupRef references an ItemGroupDef as it occurs within a specific StudyEventDef or ItemGroupDef. The list of ItemGroupRefs identifies the types of item groups that are allowed to occur within this type of studyevent or (nested) itemgroupitem group. The ItemGroupRefs within a single StudyEventDef or ItemGroupDef must not have duplicate ItemGroupOID or OrderNumber attribute values.
The MethodOID references a MethodDef used to pre-populate prepopulate items.
The OrderNumber attribute provides an ordering on the ItemGroupDefs (within StudyEventDef or ItemGroupDef) for use whenever a list of ItemGroupDefs is presented to a user. Order of execution is preferably defined in a workflow (see Section 3.2.2.1.8, WorkflowDef) but when used without a workflow, may be used the define the order in which data entry forms are presented in an application UI.
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