We want to consolidate referentGroup and variableDefinition into one backbone element, and make other changes to make the Evidence resource easier to understand and use. To refer to a group (population) in an Evidence resource we want to use the variableDefinition backbone element instead of referentGroup, and referentGroup can be deleted.

Proposed changes to the Evidence Resource structure:

1. Add “population” and “subpopulation” to the variable-role Value Set used by “variableDefintion.variableRole”
2. Change the variableDefinition.actualDefinition datatype from “Reference(EvidenceVariable)” to “Reference(Group | EvidenceVariable)”
3. Change the “variableDefinition.intendedDefinition” datatype from “Reference(EvidenceVariable)” to “Reference(Group | EvidenceVariable)”
4. Delete the “referentGroup” backbone element from the Evidence resource, and all the elements within it will be removed as well.
5. Rename “variableDefinition.actualDefinition” to “variableDefinition.observed”
6. Rename “variableDefinition.intendedDefinition” to “variableDefinition.intended”
7. The cardinality of the “variableDefinition” will change from 0..* to 1..*
8. The cardinality of “variableDefintion.variableRole” will change from 0..1 to 1..1, so it will be known what resource “observed” and “intended” will be referencing.
9. We will update all the Evidence resource examples within the FHIR build to match the changes to the resource.