Regarding how to report frequencies using the effectiveTime as a PIVL_TS or EIVL_TS: After some research and conversation, we do not think there is any specific guidance on this particular issue. While the QRDA Cat 1 base IG constrains the type to be PIVL_TS or EIVL_TS, the CMS IG is silent on the matter. Due to this lack of formal guidance, and the many variations of what can be represented, it's difficult to determine how well these complex frequencies will be supported by health IT systems. Regarding two specific questions that were raised by the submitter: - How do you say things like "with breakfast", "10 minutes before breakfast", "between meals", etc? - How do you say "every 4 - 6 hours"? Do you apply an average ("every 5 hours")? For event-based frequencies, like "before breakfast", an IVL_TS represent the period over which the medication is taken, and a EIVL_TS with an embedded event represents the timing of the medication. For example: <!-- med started on 1/18/2014 and has not ended --> <effectiveTime xsi:type="IVL_TS"> <low value="20140118"/> <!-- med started on 01/18/2014 --> <high nullFlavor="NI"/> <!-- med has not stopped --> </effectiveTime> <!-- med frequency: before breakfast --> <effectiveTime typeCode="EIVL_TS" operator="A"> <!-- where "A" stands for every --> <event code="ACM"/> <!-- where "ACM" stands for "before breakfast" --> </effectiveTime> Together, these two effectiveTimes would be understood as follows: A medication that started on 1/18/2014 and is to be taken every morning before breakfast. The event/@code uses codes from the "TimingEvent" concept domain. You can find a full list here: http://hl7.org/fhir/v3/TimingEvent/ For frequencies such as "every 4 - 6 hours", an IVL_TS represents the period over which the medication is taken, and a PIVL_TS with an embedded interval represents the timing of the medication. For example: <!-- med started on 1/18/2014 and has not ended --> <effectiveTime xsi:type="IVL_TS"> <low value="20140118"/> <high nullFlavor="NI"/> </effectiveTime> <!-- med frequency of 4 - 6 hours --> <effectiveTime typeCode="PIVL_TS" operator="A"> <!-- where "A" stands for every --> <period xsi:type="IVL_PQ"> <low value="4" unit="h"/> <-- minimum 4 hours --> <high value="6"StartFragment unit="h"/> <-- maximum 6 hours --> </period> </effectiveTime> Together, these two effectiveTimes could be understood as follows: A med that started on 1/18/2014 and is to be taken every 4 - 6 hours. Many thanks to Stan Rankins of Telligen and Rob Dingwell of MITRE, who helped us work through some of this. We hope that this helps you a bit. Let us know if you need to talk through this further.