Glossary

Case Mix Index (CMI)

Also known as: CMI, acuity index, CMI

A numeric score reflecting the average acuity and resource intensity of a skilled nursing facility's resident population, used to risk-adjust Medicaid reimbursement rates in many states and to benchmark clinical complexity across facilities.

CMI is calculated from resident assessment data (the Minimum Data Set, or MDS) and, in case-mix-adjusted Medicaid states, directly drives the facility's per diem rate -- a facility with a higher CMI (sicker, more resource-intensive residents) receives a higher Medicaid rate under those state methodologies, which creates an operating incentive to accurately and completely document resident acuity through timely, thorough MDS assessments. CMI accuracy and MDS assessment quality are therefore a specific area of operational diligence in skilled nursing acquisitions, since under-documentation can mean a facility is leaving legitimate reimbursement on the table, while a sudden unexplained CMI spike can be a red flag for audit risk.