<status value="draft"/> <description value="placebo"/> <actual value="true"/> <characteristic> <description value="placebo"/> <definitionCodeableConcept> <coding> <system value="http://snomed.info/sct"/> <code value="182886004"/> <display value="Placebo given (situation)"/> </coding> </definitionCodeableConcept> </characteristic> </EvidenceVariable>

Placebo is a specific exposure that may be used in expressing what an Evidence is about.