Within the Clinical Data Interchange Standards Consortium (CDISC) Study Data Tabulation Model (SDTM), standard domains are split into four main types: special purpose, relationships, trial design and general observation classes. General observation classes cover the majority of observations collected during a study and can be divided among three general classes:
When creating a custom domain, one should first confirm that there are no published domains available into which the data can be mapped. This can be done by checking against the reserved domain codes listed in the appendices of the current SDTM Implementation Guide or by looking through a relevant Therapeutic Area User Guide if one is available for the indication under investigation. The following is not acceptable when creating custom domains:
Once it is confirmed that the data does not fit with any published domains, it should be determined which of the three general observation classes best fits the topic of the data since the custom domain must fit in to one of these. The next step is to determine a two-letter domain code for the custom domain. This should not be the same as the code for any published or planned domain. The domain codes X-, Y- and Z- are reserved for sponsor use, where the hyphen may be replaced by any letter or number. This domain code then will be the name of the domain and will also be used to replace all prefixes of variables from the class upon which it is based. The following steps can then be followed to create the custom domain:
Variable attributes within the domain and Supplemental Qualifier datasets must conform to the SAS Version 5 transport file conventions. For example, variable names must be no longer than 8 characters, variables labels must be no longer than 40 characters and data value lengths must be no longer than 200 characters. Also, the transport file for any SDTM dataset should not exceed 5 GB in size or domains may need splitting to fulfil this requirement and the split documented in the Data Reviewer’s Guide that accompanies the submission.
Authors note: This blog was originally published on 21/07/2011 and has since been updated.
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