A new study shows patients have on average a 70 percent lower chance of dying at the nation's top-rated hospitals compared with the lowest-rated hospitals.

The study, conducted by HealthGrades, an independent healthcare ratings organization, looked at 17 procedures and conditions over the three-year span between 2005 and 2007.

While overall death rates declined during that time, the nation's best-performing hospitals were able to reduce their death rates at a much faster rate than poorly performing hospitals, resulting in large state, regional and hospital-to-hospital variations in the quality of patient care, the study found.

The study also found that if all hospitals performed at the level of five-star rated hospitals, 237,420 Medicare deaths could have been prevented over the three years studied. More than half of those deaths were associated with four conditions: sepsis (a life-threatening illness caused by systemic response to infection), pneumonia, heart failure and respiratory failure.

The HealthGrades study of patient outcomes at the nation's approximately 5,000 hospitals is the most comprehensive annual study of its kind, analyzing more than 41 million Medicare hospitalization records from 2005 to 2007. The study examines procedures and conditions ranging from heart valve-replacement surgery to heart attack to pneumonia.

The study is also the basis for HealthGrades' 2009 quality ratings for all nonfederal hospitals in the country. The ratings are available at www.healthgrades.com, a Web site designed to help individuals research and compare local healthcare providers.

Full reports on death rate trends in each of the 50 states and the District of Columbia are available in the study. And, for the first time, HealthGrades released hospital death rates for the nation's 15 largest metropolitan statistical areas.

Phoenix (5.32 percent), Houston (5.37 percent), Detroit (5.48 percent), Chicago (5.52 percent) and Los Angeles (5.78 percent) had the lowest three-year risk-adjusted mortality rates of the 15 metro areas, although none of those rates lands them in the top 15 percentile of 5.23 percent.

New York (7.6 percent), Philadelphia (7.14 percent), Boston (7.04 percent) and Atlanta (6.83 percent) were the lowest-rated of the 15 metro areas, ranking them above the national average of 6.77 percent.

The region with the lowest overall risk-adjusted mortality rates was the East North Central region (Illinois, Indiana, Michigan, Ohio, and Wisconsin), while the East South Central region (Alabama, Kentucky, Mississippi, and Tennessee) had the highest mortality rates.

The East North Central region also had the highest percentage of best-performing hospitals at 26 percent. Less than 7 percent of hospitals within the New England region were top-performing hospitals, the study said.

"Geography should not be a major factor in patients' outcomes," said Samantha Collier, HealthGrades' chief medical officer and a study author. "If our nation's hospitals are to close the quality gap and guarantee an equally high level of medical care for every patient, no matter where he or she lives, it will require a commitment by our nation and its communities to demand more from quality improvement."