Risk adjustment is a corrective tool used to level the playing field regarding the reporting of patient outcomes by adjusting for the differences in risk among specific patients. Risk adjustment also makes it possible to compare hospital and doctor performance fairly. Comparing unadjusted event rates for different hospitals would unfairly penalize those performing operations on higher risk patients (those who are sicker or have more comorbidities).
For example, if an 86 year old female with diabetes undergoes bypass surgery, there is less chance for a good outcome when compared with a healthy 40 year old male undergoing the same procedure. To take factors into account which influence outcomes, for example, advanced age, emergency operation, previous heart surgery, a risk adjusted model is used to report surgery and mortality results.
The STS National Database, which has more than 5.4 million patient records, has long used risk adjustment to provide more accurate patient outcomes. If not risk adjusted, the records of surgeons who perform operations on higher-risk patients would be unfairly penalized.