description: The population basis specifies the type of elements in the population. For a subject-based measure, this is boolean (because the subject and the population basis are the same, and the population criteria define yes/no values for each individual in the population). For measures that have a population basis that is different than the subject, this element specifies the type of the population basis. For example, an encounter-based measure has a subject of Patient and a population basis of Encounter, and the population criteria all return lists of Encounters. Note that the subject of a measure can be found in the element [subject[x].](https://hl7.org/fhir/uv/cqm/StructureDefinition-cqm-computablemeasure-definitions.html#Measure.subject[x])
package_name: hl7.fhir.uv.cqm
derivation: constraint
name: CQMPopulationBasis
type: Extension
elements:
  url:
    type: uri
    pattern: {type: Uri, value: 'http://hl7.org/fhir/uv/cqm/StructureDefinition/cqm-populationBasis'}
    index: 0
  value:
    choices: [valueCode]
    index: 2
  valueCode: {type: code, choiceOf: value, index: 3}
package_version: 1.0.0-ballot
class: extension
kind: complex-type
url: http://hl7.org/fhir/uv/cqm/StructureDefinition/cqm-populationBasis
base: http://hl7.org/fhir/StructureDefinition/Extension
version: 1.0.0