http://hl7.org/fhir/StructureDefinition/statistic-model-include-if|5.2.0

The condition under which the variable (or modelCharacteristic) will be included.\n\nThe extension can be applied to Evidence.statistic.modelCharacteristic to describe when that modelCharacteristic is included in the statistical model, or can be applied to Evidence.statistic.modelCharacteristic.variable to describe when that variable is included in the adjusted analysis.\n\nThis extension requires two elements, an attribute and a value[x]. The interpretation of the extension instance is that when the attribute VALUE matches the value[x] VALUE, then the corresponding model characteristic (or variable) element shall be included in the model.