<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.