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This section describes how the SDTM will be implemented to represent relationships between records within a domain, between records in different domains,

When applicable, variables IDVAR and IDVARVAL will represent variable and value pairs used as record-level keys to merge/join records between datasets.

• Each observation within a domain
• Groups of observations within a domain

The uniqueness of values by observation or groups of observations can be used to represent relationships efficiently. In cases where values are unique to observations, the variable represented in IDVAR will have values from collected data (e.g., --SPID, --RECID), when possible. When this is not possible, variables with derived values may also be used (e.g., --SEQ, LNKID, --LNKGRP).