Conformance Requirement 15 on the quality measure IG states:

1. For patient-based measures, the CQL stratification expression SHALL return a Boolean.
2. For event-based measures (e.g. episode-of-care), the CQLstratification expression SHALL return a list of events of the same type as the population criteria.

This change request is for relaxing the requirement 1 to allow stratification expressions to return any type that can be represented in the MeasureReport.group.stratifier.stratum.value] CodeableConcept field.

See this zulip thread] for an example of how a stratifier can return a coded value (Patient.gender) instead of a boolean, for a Patient-based measure.

Comment from Bryn on zulip:

that conformance requirement exists because that's the way that HQMF represented stratifiers. However, the underlying FHIR resources don't have that requirement and allow more flexible specification of stratifier criteria. You raise a very good point that because the underlying resources allow it, should the Quality Measure IG relax that conformance requirement. Do you mind submitting a tracker to that effect to the Quality Measure IG? We are planning on stratifiers and supplemental data being a focus of the upcoming connectathon, and would love to get feedback on that aspect.

For event-based measures, I think requirement 2 can be relaxed as well. Instead of requiring the list of events to have the same type as the population criteria, the list could have any type, as long as the length of the list is equal to the length of the population list, and in the same order.

To illustrate, here is an example for an event-based cohort measure that stratifies on Encounter.status:

// cql

```

define "Initial Population": [Encounter] E where E.period during "Measurement Period"

define "Status Stratifier": "Initial Population" E return E.status

```

// Measure.group

 
"stratifier": [
{
"code":

,
"criteria":

}
]

// MeasureReport.group
"stratifier": [
{
"code": [

],
"stratum": [
{
"value":

,
"population": [
{
"code": {
"coding": [

]
},
"count": 50
}
]
},
{
"value":

,
"population": [
{
"code": {
"coding": [

]
},
"count": 50
}
]
}
]
}
]