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The Related Records (RELREC) special-purpose dataset is used to describe relationships between records for a subject in different datasets and relationships between datasets. RELREC will not be used to represent relationships already represented in Supplemental Qualifier (SUPP--) datasets for nonstandard variables or the Comments (CO) dataset for unstructured free-text.

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Relationships between records for a subject in different datasets are specified using the key variables STUDYID, RDOMAIN, and USUBJID, along with IDVAR and IDVARVAL (the value of the identifying variable). IDVARVAL will contain the value of the variable described in IDVAR. Single records can be related by using a unique-record-identifier variable such as --SEQ in IDVAR. Groups of records can be related by using grouping variables such as --GRPID in IDVAR.  Using --GRPID can be a more efficient method of representing relationships in RELREC when relating a single or group of records in one dataset to a group of records in another dataset. Variable RELTYPE will not be used when relating records for a subject and is only used when representing relationships between datasets. The value of RELID will be identical for all related records within USUBJID.

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