Agree with recommendation.  Will update the description in the population basis extension ( https://hl7.org/fhir/us/cqfmeasures/2024Jan/StructureDefinition-cqfm-populationBasis.html) as follows (changes highlighted in red) 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/us/cqfmeasures/2024Jan/StructureDefinition-computable-measure-cqfm-definitions.html#Measure.subject[x]]" 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.