Element C, Define Methodology requires the organization to have a method for determining measurement error and measure reliability. Element D, Adhere to Key Principles sets requirements for minimum observations or levels of measure reliability or confidence intervalsas applicable for quality and cost, resource use or utilization measures. For calculating measure reliability for PHQ, the organization must use the method described in the Explanation in Element C under the subhead Measurement Error. Measure reliability is defined as the ratio of the variance between physicians to the variance within one physician, plus the variance between physicians. NCQA does not prescribe the method used to calculate confidence intervals because the appropriate method may vary based on the parameter (e.g., mean or proportion).