When nursing CMI rises… and stars fall
Understanding how nursing case-mix index, hours per resident per day, census, and staff turnover interact is essential for nursing homes trying to manage their Five-Star staffing rating, as even small shifts in CMI can have outsized effects on a facility's score in ways that are easily misinterpreted.
Today’s column could be given the subheading: “Understanding the connection: CMI and staffing star ratings.”
We regularly hear questions about how nursing Case-Mix Index (CMI) influences CMS’ Five-Star Quality Rating System’s staffing rating in our work at Zimmet Healthcare. And it’s no surprise. This relationship is nuanced, easily misinterpreted, and highly sensitive to subtle shifts in data.
To bring clarity, we explore three scenarios — all real — and each grounded in recent data. If you’re looking to build more context, I recommend reviewing this earlier article: Does payer mix impact nursing case-mix index?
National Averages (May 2025)
- Reported Total Nurse Hours per Resident per Day (HPRD): 3.8647
- Nursing Case-Mix Index (CMI): 1.36761
- Average Staffing Star Rating: 2.82
Note: To simplify these examples, staff turnover is held constant. In reality, turnover plays a role in final staffing ratings.
Where data meets reality
Below you’ll see a graph that illustrates how Nursing CMI, HPRD and Five-Star staffing rating relate.
“Once we mapped out how CMI, HPRD and Staffing Ratings interact, the complexity of the system became much more apparent. It’s especially sensitive in the range where most nursing homes cluster (3.8647 HPRD) — small changes in CMI can have outsized effects on a facility’s star rating,” said Chasey Sanchez, EdD, Director of Healthcare Analytics, Zimmet Healthcare
Scenario 1:
“We’ve been assigned a 1-star staffing rating, and consequently, I lost one star in my Overall rating. How much staff do I need to add to move up to a 2-star staffing rating?”
Assumptions:
- Your CMI is near the national average (~1.37)
- Turnover is average
To move up to a 2-star rating, you’d need to report at least 3.12 HPRD.
Facilities with a slightly lower CMI can get by with fewer hours, while those with higher acuity must increase HPRD just to maintain their current rating. The table below is set to a staffing rating of greater than or equal to 2 stars.
Scenario 2:
“We’re aiming for 5 stars in the Staffing domain. What does it take?”
Assumptions:
- CMI ~ 1.37
- Turnover is average
According to May 2025 data, to achieve a 5 star staffing rating, you generally need:
- A lower CMI between 1.1 and 1.33
- HPRD of 3.8647 or higher
But accurate MDS and PBJ data are essential. I’d love to be a fly on the wall when you tell your CFO that you’d like to lower your CMI.
But there are outliers to the above. Here is what we found in the CMS data:
This paints a clearer picture: High star staffing ratings are often tied to moderate acuity and robust staffing.
Scenario 3:
“We’re currently a 2 star in staffing. How low can our staffing go without dropping to 1 star?”
Assumptions:
- CMI ≈ 1.367
To maintain your 2 star rating, your HPRD must remain above 3.1062. This threshold leaves little room for variability.
The “green zone” is narrow … Understanding where you fall helps you stay ahead of unwanted rating drops.
Key takeaways: What actually moves the needle?
When it comes to your staffing star rating, there are four primary levers you can influence:
- Nursing Case-Mix Index (CMI): Reflects the clinical acuity of residents.
- Reported nurse Hours Per Resident Per Day (HPRD): Indicates staffing intensity.
- Census: Average daily resident count, as reported on PBJ.
- Staff turnover: Especially among RNs and total nursing staff, which can compound risk over time.
While turnover plays a key role — particularly at the margins — CMI, HPRD, and census are the foundational elements that determine your staffing star.
And it bears repeating:
Staffing to a budget is not a strategy. Staffing to resident acuity (needs) and to census is.
In an environment shaped by staffing challenges and reimbursement limitations, these insights can help guide smarter, more realistic and resilient decisions.
Steven Littlehale is a gerontological clinical nurse specialist and Chief Innovation Officer at Zimmet Healthcare Services Group.
The opinions expressed in McKnight’s Long-Term Care News guest submissions are the author’s and are not necessarily those of McKnight’s Long-Term Care News or its editors.
