Study ranks states based on hospital performance

Healthgrades also ranked states based on their hospitals' success with the four conditions that account for most U.S. deaths — coronary artery bypass grafts, heart attacks, pneumonia and sepsis.

Patients in Arizona, California, Illinois and Ohio hospitals are most likely to survive those conditions, Healthgrades found. Those in Alabama, Arkansas, Georgia, Nevada, Oklahoma, Washington, D.C., and West Virginia hospitals are least likely to survive.

Healthgrades did not speculate about why some states' hospitals do better. The report noted hospital quality can vary widely within states and that Healthgrade rankings do not reflect the quality of every institution.

"For instance, if you suffer a heart attack in the city of Chicago, depending which hospital the ambulance takes you to, you face as much as an 11-fold higher mortality rate in one hospitals versus another on the other side of town," researchers wrote. "Taken together, these factors make it critical for consumers to compare how well hospitals and doctors are performing when treating patients."

Patients are 55 percent less likely to die and 42 percent less likely to have a complication when treated in the best hospitals, the report found.

Hospital mortality rates are calculated by dividing the number of patients who die from a certain condition or procedure by the number of patients admitted for that condition or procedure.