The measure developer must explicitly state in the measure specification when they use intervals to determine cases for inclusion in the denominator, numerator, denominator exclusion, or numerator exclusion. The measure developer must clearly indicate the index event used to determine the time intervals. Also, the specification must identify how often to report the numerator for each patient as well as how often to include a patient in the denominator. For example, if a patient has three episodes of pneumonia during the measurement period, should the numerator include each episode?

Measure developers must

• Avoid using ambiguous semantics when specifying time intervals.
• State the exact interval units required to achieve sensitivity necessary for measurement.
• State the exact interval units required to achieve the level of granularity necessary to ensure validity and reliability of the measure calculation.
• Explicitly state any look-back periods. For example, the Breast Cancer Screening measure looks back 27 months prior to the end of the measurement period for an individual's history of a bilateral mastectomy or both a right and left unilateral mastectomy. Both are denominator exclusions.

International Organization for Standardization 8601:2004 defines data elements and interchange formats for the representation of dates and times, including time intervals. The Health Level Seven International® Clinical Quality Language specification, Appendix H also provides conventions with the intent to standardize time calculation units for durations (e.g., difference between two date/time elements). The measure developer should use these standards in time interval calculations for any type of quality measure, not just electronic clinical quality measures.

Example

• Perform medication reconciliation within 30 days following hospital discharge. Thirty (30) days is the time interval, and the hospital discharge date is the index event. If the minimum sensitivity and level of granularity desired was one month instead of 30 days, then the measure specification should state “month” instead of “day” as the unit of time. However, as the length of a month is variable by month, it is preferable to express time intervals in terms of days.