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Grouping variables are a subset of Identifier and Grouping Qualifier variablesused to group records in datasets . Hierarchy of Grouping by study, domain, across subjects, by subject, and for a subject. When used per this guidance, grouping variables and their values adhere to the following hierarchy:

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How Grouping Variables Group Data

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1. All records with the same USUBJID value are a group of records that describe that subject.

The following are expectations for how values in these variables will group records given their hierarchy.

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1. --GRPID values further group (subset) records within USUBJID. Unlike --CAT and --SCAT, --GRPID values are not intended to have any meaning across subjects and they are usually assigned during or after data collection.
2. Although --SPID and --REFID are identifier variables, these are usually not considered to be grouping variables, although they may have meaning across domains.

The optional grouping identifier variable --GRPID may be used in all domains based on the general observation classes. --GRPID identifies relationships between records within a USUBJID within a single domain and has no inherent meaning across subjects or across domains. Relationships between observations are defined by assigning the same unique character value to the --GRPID variable for sets of related observations. The values used for --GRPID can be any values the applicant chooses. --GRPID values are not intended to have any meaning across subjects and are usually assigned during or after data collection.

Using --GRPID in the general-observation class domains can reduce the number of records in the RELREC, SUPP--, and CO datasets, when those datasets represent relationships/associations for records or values to a "group" of general observation class records.

Differences Between Grouping Variables

1. The primary distinctions between -CAT/ SCAT and --GRPID are:
   1. --CAT/ SCAT are known (identified) about the data before it is collected. --CAT/ SCAT values group data across subjects. --CAT/-SCAT may have some controlled terminology.
   2. --GRPID is usually assigned during or after data collection at the discretion of the sponsor. --GRPID groups data only within a subject. --GRPID values are sponsor-defined and are not be subject to controlled terminology.
2. The primary distinction between -CAT/ SCAT and --REFID is that --CAT/-SCAT are usually textual descriptions of the data designed into the collection vehicle/process, and --REFID is usually a tracking number/value of some type assigned to an object being tracked (e.g., a blood sample).

In domains based on the Findings general observation class, the --RESCAT variable can be used to categorize results after the fact. --CAT and --SCAT by contrast, are generally predefined or used at the point of collection, not after assessing the value of findings results.