Delayed because the American Hospital Association doesn't want you to know how dangerous some hospitals might be to your health - even survival, - a long awaited study on what the government terms "adverse events" in hospitals has been released by HHS.

Its conclusions will shock you:

Of 1 million elderly and disabled Medicare patients hospitalized annually, 13.5 percent - or 135,000 people - experience an adverse event, with associated costs of $4.4 billion, according to a November 2010 report from the inspector general of the U.S. Department of Health and Human Services. Among people of all ages, hospital errors account for nearly 100,000 deaths each year, according to the Institute of Medicine, an arm of the National Academy of Sciences.

Information included in the new Medicare patient safety report came from medical bills submitted by hospitals to Medicare for payment - a data source that several experts said is flawed and subject to "coding" errors. With each Medicare invoice, medical conditions treated are given a code that determines the payment amount.

While coding mistakes are common, ensuring that bills accurately reflect medical information is hospitals' responsibility, other experts noted. Also, since 2008, Medicare has refused to pay for complications associated with several adverse events, giving hospitals a strong incentive to check coding practices.

The American Hospital Association opposed the release of the Medicare report on so-called adverse events, which had been scheduled last fall but was delayed because of industry concerns. In an interview, Nancy Foster, vice president of quality at the hospital association, said it "is not a reliable reflection of patient safety issues in hospitals." Objections of this kind aren't new; hospitals often complain when Medicare releases reports about the quality of medical care.

But officials say the government is committed to shining a light on things that go wrong in hospitals, often because of poor communication between providers, inadequate follow-up or other breakdowns in the processes of care.