http://hl7.org/fhir/StructureDefinition/iso21090-uncertainty|5.2.0

The primary measure of variance/uncertainty of the value (the square root of the sum of the squares of the differences between all data points and the mean).
typedestination
baseDefinitionhttp://hl7.org/fhir/StructureDefinition/Extension
typehttp://hl7.org/fhir/StructureDefinition/Extension
Extension.value[x].typehttp://hl7.org/fhir/StructureDefinition/decimal