# Denominator Exclusions

Denominator exclusions refer to criteria that result in removal of patients or cases from the denominator before calculating the numerator. A denominator exclusion means the numerator event is not applicable to those covered by the denominator exclusion; an example of a denominator exclusion is to “exclude women who have had bilateral mastectomy from the denominator for a measure of screening mammography.”

The goal of denominator exclusion criteria is to have a population or sample, all of whom share a similar profile in terms of their likelihood of meeting the numerator criteria.

**Format:** denominator-eligible patients who [have some additional characteristic, condition, procedure]

The measure developer must not specify systematically missing data as a denominator exclusion. The CMS consensus-based entity (CBE) Consensus Standards Approval Committee *Guidance on Quality Performance Measure Construction* notes systematic missing data (e.g., when poor performance is selectively not reported) reduce validity of conclusions that can be made about quality.

To avoid complexity, the measure developer should limit denominator exclusions to just those that are absolutely necessary. Ensure the measure logic expressions (e.g., Clinical Quality Language) clearly identify denominator exclusions. The measure developer should support an allowable denominator exclusion with

- Evidence the denominator exclusion condition occurs with such frequency that it will distort the measure results without the denominator exclusion, and
- Evidence the denominator exclusion significantly improves measure validity, and/or
- Evidence of both empiric and face validity.

Also consider

- Conditions present on admission should not count as an outcome of interest.
- An outcome of interest can be very difficult to prevent in a population of interest, and therefore not an indication of substandard care.
- Some inclusion criteria identify populations who are at very low risk for the outcome of interest, but then the measure developer incorrectly made a denominator exclusion to prevent dilution of the quality improvement denominator.
- Some inclusion criteria are for the purpose of enhancing face validity with clinicians.
- Some inclusion criteria are an inherent part of the quality improvement definition.
- The inclusion criteria may conflict with the patient’s goals of care (e.g., advanced illness, terminally ill).

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