What is the CMS hospital star rating?

The overall rating is a single 1–5 score built from five groups of quality measures.

The five groups

CMS groups dozens of measures into mortality (deaths among patients treated for serious conditions), safety of care (infections and complications), readmission (patients returning soon after discharge), patient experience (survey responses about communication and the stay), and timely & effective care (how quickly and appropriately care is delivered). Each group is summarised as better than, no different from, or worse than the national average.

How the star rating is derived

Groups are weighted and combined into a summary score, then compared with other hospitals. A hospital rated 5 stars performs better than most on most groups; 1 star means worse. The rating reflects reported measures, not the size of the building or the reputation of the doctors.

Why many hospitals are unrated

A hospital needs enough measures in at least three groups to be rated. Small rural hospitals, specialty hospitals (children's, psychiatric, rehabilitation) and facilities with low case volumes often fall below the threshold, so "not rated" does not mean poor quality.