What does Case Mix Index (CMI) measure and how does it impact payment?

• A. CMI measures hospital staffing efficiency; higher CMI reduces payment.
• B. CMI reflects average length of stay; higher CMI lowers payment.
• C. CMI reflects average DRG weights for a patient population; higher CMI leads to higher payments.
• D. CMI tracks patient satisfaction scores; higher CMI increases penalties.

Answer: (C)

Case Mix Index measures the resource intensity of a hospital’s patient population as captured by DRG weights. Each admission is assigned a DRG with a relative weight that reflects the typical cost and resource use for that episode. The CMI is the average of those weights across all cases, so hospitals with more high-weight DRGs have a higher CMI. In DRG-based payment systems, payments are proportional to DRG weight times a base rate, so a higher CMI means higher total payments because the hospital is treating more complex, more costly cases. It isn’t a measure of staffing efficiency, nor a direct reflection of average length of stay, and it doesn’t track patient satisfaction or penalties—those are separate aspects of payment and quality.