The QDM attribute, negation rationale indicates the reason that an action was not performed. Only QDM datatypes that represent actions (e.g., performed, recommended, communication, order, dispensed) allow the 'negation rationale' attribute. The intent is to indicate a justification that such action did not happen as expected. This attribute specifically does not address the presence or absence of information in a clinical record (e.g., documented absence of allergies versus lack of documentation about allergies). QDM assumes that any information expected will be in a clinical record. The situation is different when something that normally would be expected to be done is specifically not done because of a valid clinical reason (such as the patient is allergic, they are suffering from a complication, or some other rationale. In this case, the 'thing not done' is rarely documented, especially as a code, in the patient record. To express such lack of evidence, an eCQM author should use a CQL 'not exists' expression noted in the examples, and they must also capture the Negation rationale to capture a reason for the absence, i.e., the reason must be included to qualify as a negation rationale type expression. The syntax in the human readable HQMF is described in CQL examples and in the MAT User Guide. Prior versions of QDM used the syntax, 'Procedure, Performed not done.' QDM 5.5 uses the syntax, 'Procedure, not Performed' and this is then associated with either a DRC or a value set used to identify 'the expected thing,' that in this case was not done. Negation Rationale attribute value indicates a one-time documentation of a reason an activity is not performed. Negation of QDM datatype-related actions for a reason always use the author dateTime attribute to reference timing.