The “overlaps” timing operator provides a way that two data elements defined in the measure can be compared temporally to determine if there is any overlap in time between the two data elements. While there are currently timing operators that provide some functionality to define concepts similar to overlap, they require multiple statements of logic to construct the most common manifestation of overlap required in the logic. The existing approach has been to define overlap using specific occurrences and two logical statements. This approach is described in the eCQM logic guidance document. That document recommends expressing overlap as follows:

AND:      Occurrence A of X starts before or during Occurrence A of Y
AND NOT:  Occurrence A of X ends before start of Occurrence A of Y

The need for multiple logical statements and specific occurrences stems from the definition of the “during” operator and the way null dates are treated for a time interval that has not yet ended. The “during” operator requires, for X to be during Y, X must start after or concurrent with the start of Y, and X must end before or concurrent with Y. Therefore, X during Y does not define an overlap where two events share a common time interval, but one event is not contained within the timing of the other. Additionally, the definition of timing calculations in the case of a null end date causes the “during” operator to evaluate to false because a date cannot start before or be concurrent with a null date. These conditions cause the implementation of the overlaps construct to require the logical construct above.

The introduction of an overlaps operator that handles null end dates as part of the overlap would eliminate many instances of the above construct in existing measures. The above logic could then be re-written as:

AND: X overlaps Y

There would no longer be a need for multiple logical statements, a negated statement, or specific occurrences. Additionally, if either X or Y had null start or end dates, the evaluation of X overlaps Y would evaluate equivalently with the original logical statements above. In other words, as long as X starts before the end of Y and X does not end before the start of Y (including a null end date on X), then overlaps would evaluate to true. Existing temporal indicators would not require modification as a result of introducing the recommended overlap timing indicator to the QDM.