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Each form belongs to a study event, and can be identified (within that study event) by a FormOID (which gives its type) and a FormRepeatKey.
Collected data always belongs to an ItemGroup but two forms of the hierarchy maybe used within a Clinical Data element.
Each item group in clinical data belongs to a form, and can be identified (within that form) by an ItemGroupOID (which gives its type) and an ItemGroupRepeatKey.
Other items groups are reference data, and can be identified solely by an ItemGroupOID and an ItemGroupRepeatKey.
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