Negation has several aspects: (a) assurance that a certain condition does not exist (e.g., no known allergies); (b) lack of evidence that a condition exists (e.g., no information is available in the electronic health record about allergies); and (c) that a measured entity intentionally did not perform an action, with or without a reason (e.g., the clinician did not prescribe the medication due to interaction with other medications a patient is taking). The QDM negation rationale attribute addresses only the third definition, sometimes called action negation. The QDM includes this concept as negation rationale as an attribute of the QDM datatypes. Its inclusion allows a measure developer to express a measure criterion or a measure exception if the clinician expressed a reason for not performing the action expected. The QDM documentation on the eCQI Resource Center describes how a measure developer can use negation rationale. Negation rationale is part of v.5.5 Guidance Update for the 2021 and 2022 reporting/performance periods, and v5.6 for the 2023 reporting/performance period.