Given a qualifying performed procedure, how do I determine the admission date for that performed procedure? Can Procedure, Performed's relevantPeriod attribute be used as the index admission (i.e. Admission Date) and post index of admission (i.e. discharge date) OR I have to join with Encounter, Performed on relevantPeriod attributes and then use the matching Encounter, Performed's relevantPeriod attribute for index of admission? Below are my CQL expressions and your suggestion is very much appreciated. define "Qualifying Procedures": ( ["Procedure, Performed": "Hip Replacement Surgery"] union ["Procedure, Performed": "Knee Replacement Surgery"] ) Procedure where Procedure.relevantPeriod during "Measurement Period" define "Qualifying Encounters For Procedure": ["Encounter, Performed": "Encounter Inpatient"] ValidEncounter with "Qualifying Procedures" ProcedureDate such that ValidEncounter.relevantPeriod overlaps ProcedureDate.relevantPeriod Regards, TT