Hospital Star Rating

Key facts

Publisher

CMS, on Medicare Care Compare

First released

July 2016

Scale

1 to 5 stars

Measure groups

Mortality, Safety of Care, Readmission, Patient Experience, Timely and Effective Care

Star assignment

k-means clustering of summary scores within peer groups

What is the hospital star rating?

CMS publishes many individual quality measures for hospitals, which are hard to interpret one by one. The Overall Hospital Quality Star Rating condenses them into a single number of stars. It covers hospitals that report through CMS quality programs, mainly acute care hospitals, along with Critical Access Hospitals that report voluntarily.

The rating is separate from other CMS star programs. Patient survey star ratings based on HCAHPS appear alongside it, and nursing homes, dialysis facilities, home health agencies and Medicare Advantage plans each have their own star systems with different methods.

How the star rating is calculated

CMS adopted the current methodology in 2021. It works in steps:

CMS adjusts the method through rulemaking, so ratings from different release years are not strictly comparable.

• Measures are standardized and assigned to five groups: Mortality, Safety of Care, Readmission, Patient Experience, and Timely and Effective Care.
• Each group score is a simple average of its measure scores, and the summary score is a weighted average of group scores in which Timely and Effective Care carries less weight than the other four groups.
• A hospital is rated only if it reports at least three measures in each of at least three groups, one of which must be Mortality or Safety of Care.
• Hospitals are placed in peer groups by how many measure groups they report (three, four or five), and k-means clustering within each peer group assigns stars.

Why the star rating matters

Star ratings are widely cited but need careful interpretation:

• Health systems cite star ratings in marketing and benchmarking, and payers and employers may use them in network and referral decisions.
• Many hospitals, especially small and rural ones, receive no rating because they report too few measures. An unrated hospital is not a one-star hospital.
• Underlying measures cover periods that lag the release by months to years, so ratings describe past performance.
• Joining star ratings to cost report and claims data by CMS Certification Number lets analysts relate quality to size, payer mix and procedure volume.