Case mix index is calculated by dividing the total MS-DRG relative weights by the number of discharges:
1,750 รท 1,000 = 1.75
Therefore, the hospital's CMI is 1.75.
CMI is an aggregate measure representing the average relative resource intensity of the hospital's inpatient population under the MS-DRG system. A higher CMI generally indicates that the hospital treated cases assigned to DRGs with higher average relative weights.
However, CMI should never be interpreted as a pure measure of clinical quality. It can be affected by patient population, service-line composition, surgical volume, transplant activity, documentation completeness, coding accuracy, changes in grouper methodology, and other factors.
CMS specifically publishes hospital CMI data and uses MS-DRG relative weights in the IPPS payment methodology. CMS also maintains FY 2026 case-mix and relative-weight files as part of the final-rule data package.
For CDI program analysis, unexplained CMI changes should trigger investigation rather than an automatic assumption of poor documentation. Service-line and diagnosis-level analysis usually provides a more meaningful interpretation.
CCDS Reference Topics: Case mix index; relative weights; CDI analytics; MS-DRGs; program performance.
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