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If data are in scope for a domain defined in this guide , but not all data can be collected using the domain's collection fields, then collection fields may be added to the applicant's CRF from the CDASH Model, the SDTM, or created by the applicant using guidance belowin the TIG.

Prior to adding fields from the CDASH Model, the SDTM, or considering a new applicant-defined collection field, confirm that none of the fields in the domain will fit the need. Fields may be added from the CDASH Model, the SDTM, or created only when data are different in nature and are not in scope for collection fields in this guide. Once confirmed, determine whether adding a field from the CDASH Model will fit the need or, if not, whether using a variable from the SDTM will fit the need. If adding a field from the CDASH Model or SDTM meets the need, then a new field will not be created. New fields will only be created when data are not in scope for a field defined in the CDASH Model or a variable defined in the SDTM.

Once confirmed, the overall process for extending metadata is as follows:

Using the root variables and other CDASH metadata in the CDASH Model, add any additional variables that are needed to meet the requirements of data collection.
1. Refer to both the CDASH Model and Appendix xC, CDASH Model Metadata Tables.
2. Follow CDASH root variable-naming conventions where they exist (e.g., --DAT for dates, --TIM for times, --YN for prompts, as described in the CDASH Model) and align with Appendix x, CDISC Variable-naming Fragments, conventions CDISC NSV Registry conventions as applicable.
Select variables from the SDTM when fields from the CDASH Model cannot be used. Selection of variables must align with SDTM Usage Restrictionsusage restrictions.
Create a new data applicant-defined collection field when when fields in the CDASH Model and variables from the SDTM cannot be used.
1. When creating a new data applicant-defined collection field, determine whether the data will be used for an operational use case (e.g., such as data cleaning, ) or are actual data to be represented in a tabulation dataset. In general, new data collection fields (not already defined in the CDASH Model) will fall in one 1 of following categories:
  1. A a field used for operational, Data Cleaning data cleaningpurposes only.;
  2. A a field used to collect data that have Direct Mapping direct mappingto a target variable in the tabulation dataset.; or
  3. A a field used to collect data that have No Direct Mapping no direct mapping to a target variable in the tabulation dataset.
2. The following table below provides implementation guidance aligned with both the category of the field and target variable.

Metadataspec

Num	Field Category	Target Tabulation Variable	Implementation
1	Data Cleaningcleaning	NA	The field --YN with Question Text "Were there any [interventions/events/findings]?" can be used for this purpose. Replace the two 2 dashes (--) with the two2-character domain code and create the Question Text question text or Prompt prompt using generic Question Text question text or Prompt prompts from the CDASH Model as a base. Always create custom data-cleaning/operational variables using consistent naming conventions.
2	Direct Mappingmapping	Yes	If a value can be collected exactly as it will be reported in the tabulation dataset (i.e., same value, same data type, same meaning, same controlled terminology), the tabulation variable name will be used as the data collection variable name in the operational database to streamline the mapping process. Extensions Characters may be appended if to the data collection variable name if needed to create a unique variable name in the collection database. Any collection variable whose meaning is the same as tabulation variable will align with tabulation variable and the meaning will not be modified for data collection.
3	No Direct Mappingdirect mapping	Yes	If a value cannot be collected in alignment with the tabulation dataset variable (e.g., collected data type is different from the data type in the corresponding tabulation variable) or if the tabulation variable is derived from the collected value, then the operational database should use a collection variable with a different name from tabulation variable into which it will be mapped.
3	No Direct Mappingdirect mapping	No	If a field does not align with a tabulation variable, a unique name should be assigned based on applicant business rules using CDASH naming fragments (e.g., --DAT, --TIM) as appropriate and CDISC variable naming fragments, found in Appendix x, CDISC Variable-naming Fragments, where possible. the CDISC NSV Registry, where possible.

If data are not in scope for a domain in this guide, a custom domain can be used. An existing domain may help in selecting the fields and terminology needed for the custom domain. The custom domain must be based on one of the SDTM general observation classes. See Section 2.8.3 How to Create New Specifications for further information.

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