How should the "age at" operator apply to patients whose birthday is the first day of the measurement period? For example, consider a measurement period of calendar year 2016 (ie. 1/1/2016 - 12/31/2016). If the age criteria is Age >= 18 year(s) at: "Measurement Period" then would you include a patient who turned 18 on 1/1/2016 (ie. a patient whose date of birth was 1/1/1998)?

Our interpretation has been that you would not include this patient. This was partially based on the previously used "starts before start of" syntax. QDM-12 indicates that the "Age At" operator was developed as a shorthand for expressions like Patient Characteristic Birthdate: birth date” >= 18 year(s) starts before start of "Measurement Period". I read this as saying that the patient's 18th birth date must occur before the start of the measurement period.