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A custom domain may only be created if the data are different in nature and do not fit into an existing published domain. If data collected or derived cannot be represented in a dataset defined in this guide, then a custom dataset may be used. It is recommended that a specification with the dataset name, record structure, and a domain table specification be drafted prior to implementation, but this is not required. 

In general, all domains based on the 3 general observation classes should have at least 1 timing variable.

Timing variables (SDTM Section 3.1.5, Timing Variables for All Classes) are an essential component of all SDTM subject-level domain datasets. In general, all domains based on the 3 general observation classes should have at least 1 timing variable. In the Events or Interventions general observation class, this could be the start date of the event or intervention. In the Findings observation class, where data are usually collected at multiple visits, at least 1 timing variable must be used.

Custom domain specifications and, by extension, custom datasets should be designed in the following steps:

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