# CQM Population Basis - Quality Measure Implementation Guide v2.0.0-ballot

## Extension: CQM Population Basis 

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])

**Context of Use**

**Usage info**

**Usages:**

* Use this Extension: [CQM Computable Measure](StructureDefinition-cqm-computablemeasure.md) and [CQM Ratio Measure](StructureDefinition-cqm-ratiomeasure.md)
* Examples for this Extension: [Bundle/EmergencyCapacityReportingExample](Bundle-EmergencyCapacityReportingExample.md), [BCSComponent](Measure-BCSComponent.md), [BedCapacityMeasureDaily](Measure-BedCapacityMeasure-daily.md), [BedCapacityMeasureMonthly](Measure-BedCapacityMeasure-monthly.md)... Show 19 more, [CAUTIRateExample](Measure-CAUTIRateExample.md), [CAUTISIRExample](Measure-CAUTISIRExample.md), [CCSComponent](Measure-CCSComponent.md), [EXM108](Measure-EXM108-FHIR.md), [EXM124](Measure-EXM124-FHIR.md), [EXM125](Measure-EXM125-FHIR.md), [EXM130](Measure-EXM130-FHIR.md), [EXM146](Measure-EXM146-FHIR.md), [EXM55](Measure-EXM55-FHIR.md), [MeasureEXM](Measure-EXMLogic-FHIR.md), [EXMRatioMeasure](Measure-EXMRatio-FHIR.md), [HBPComponent](Measure-HBPComponent.md), [MultiRateExample](Measure-MultiRateExample-FHIR.md), [PVSComponent](Measure-PVSComponent.md), [SupportingEvidenceExample](Measure-SupportingEvidenceExample.md), [TSCComponent](Measure-TSCComponent.md), [Terminology_FHIR](Measure-Terminology-FHIR.md), [MeasureAgeStratifiedExample](Measure-age-stratified-example.md) and [PublishableMeasureEXM](Measure-measure-publishable-exm.md)

You can also check for [usages in the FHIR IG Statistics](https://packages2.fhir.org/xig/hl7.fhir.uv.cqm|current/StructureDefinition/cqm-populationBasis)

### Formal Views of Extension Content

 [Description Differentials, Snapshots, and other representations](http://build.fhir.org/ig/FHIR/ig-guidance/readingIgs.html#structure-definitions). 

 

Other representations of profile: [CSV](../StructureDefinition-cqm-populationBasis.csv), [Excel](../StructureDefinition-cqm-populationBasis.xlsx), [Schematron](../StructureDefinition-cqm-populationBasis.sch) 



## Resource Content

```json
{
  "resourceType" : "StructureDefinition",
  "id" : "cqm-populationBasis",
  "extension" : [{
    "url" : "http://hl7.org/fhir/StructureDefinition/structuredefinition-wg",
    "valueCode" : "cqi"
  },
  {
    "url" : "http://hl7.org/fhir/StructureDefinition/structuredefinition-fmm",
    "valueInteger" : 4,
    "_valueInteger" : {
      "extension" : [{
        "url" : "http://hl7.org/fhir/StructureDefinition/structuredefinition-conformance-derivedFrom",
        "valueCanonical" : "http://hl7.org/fhir/uv/cqm/ImplementationGuide/hl7.fhir.uv.cqm"
      }]
    }
  },
  {
    "url" : "http://hl7.org/fhir/StructureDefinition/structuredefinition-standards-status",
    "valueCode" : "trial-use",
    "_valueCode" : {
      "extension" : [{
        "url" : "http://hl7.org/fhir/StructureDefinition/structuredefinition-conformance-derivedFrom",
        "valueCanonical" : "http://hl7.org/fhir/uv/cqm/ImplementationGuide/hl7.fhir.uv.cqm"
      }]
    }
  }],
  "url" : "http://hl7.org/fhir/uv/cqm/StructureDefinition/cqm-populationBasis",
  "identifier" : [{
    "system" : "urn:ietf:rfc:3986",
    "value" : "urn:oid:2.16.840.1.113883.4.642.40.61.42.21"
  }],
  "version" : "1.0.0",
  "name" : "CQMPopulationBasis",
  "title" : "CQM Population Basis",
  "status" : "active",
  "experimental" : false,
  "date" : "2026-04-07T02:06:45+10:00",
  "publisher" : "HL7 International / Clinical Quality Information",
  "contact" : [{
    "telecom" : [{
      "system" : "url",
      "value" : "http://www.hl7.org/Special/committees/cqi"
    }]
  }],
  "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])",
  "jurisdiction" : [{
    "coding" : [{
      "system" : "http://unstats.un.org/unsd/methods/m49/m49.htm",
      "code" : "001"
    }]
  }],
  "purpose" : "A measure specification needs to be able to specify the expected result type of each population criteria. This value SHALL be consistent with the result type of all population-level criteria in the measure.",
  "fhirVersion" : "4.0.1",
  "mapping" : [{
    "identity" : "rim",
    "uri" : "http://hl7.org/v3",
    "name" : "RIM Mapping"
  }],
  "kind" : "complex-type",
  "abstract" : false,
  "context" : [{
    "type" : "element",
    "expression" : "Measure"
  },
  {
    "type" : "element",
    "expression" : "Measure.group"
  },
  {
    "type" : "element",
    "expression" : "Measure.group.population"
  }],
  "type" : "Extension",
  "baseDefinition" : "http://hl7.org/fhir/StructureDefinition/Extension",
  "derivation" : "constraint",
  "differential" : {
    "element" : [{
      "id" : "Extension",
      "path" : "Extension",
      "short" : "What type of population",
      "definition" : "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.",
      "comment" : "In Health Quality Measure Format, this was referred to as the Item Count metadata attribute. If the populationBasis is specified as a data requirement, the type SHALL be present, profile and codeFilter MAY be present, and no other elements are allowed. This usage allows population basis to be stated with more specificity, e.g. CT Scans, rather than just DiagnosticReport.",
      "min" : 0,
      "max" : "*",
      "constraint" : [{
        "key" : "popBasis-1",
        "severity" : "error",
        "human" : "If DataRequirement.type is present, it may only contain the elements 'profile' and 'codeFilter'.",
        "expression" : "value.exists() and value.is(DataRequirement) implies (  value.as(DataRequirement).type.exists() and  value.as(DataRequirement).limit.empty() and  value.as(DataRequirement).sort.empty() and  value.as(DataRequirement).dateFilter.empty() and  value.as(DataRequirement).subject.empty() and  value.as(DataRequirement).mustSupport.empty())"
      }]
    },
    {
      "id" : "Extension.url",
      "path" : "Extension.url",
      "type" : [{
        "code" : "uri"
      }],
      "fixedUri" : "http://hl7.org/fhir/uv/cqm/StructureDefinition/cqm-populationBasis"
    },
    {
      "id" : "Extension.value[x]",
      "path" : "Extension.value[x]",
      "type" : [{
        "code" : "code"
      },
      {
        "code" : "DataRequirement"
      }],
      "binding" : {
        "strength" : "required",
        "description" : "The type of elements in the population",
        "valueSet" : "http://hl7.org/fhir/ValueSet/all-types"
      }
    }]
  }
}

```
