is no doubt that their occurrence is a serious matter warranting attention. The risks to public safety—and the opportunities for large-scale improvements—are sizable.

To Err Is Human focuses primarily on inpatient injuries arising as a direct consequence of treatment (errors of commission, such as prescribing a medication that has a potentially fatal interaction with another drug the patient is taking). Since the release of that report, major studies have been published substantiating serious shortcomings in other care settings and involving errors of omission (such as failing to prescribe a medication from which the patient would likely have benefited; see Table 1-1). For example, many adverse drug events occur in ambulatory care settings and in nursing homes, as well as in hospitals. A large cohort study of all Medicare enrollees cared for by a major multispecialty group practice during a 12-month period (1999–2000) identified 1,523 adverse drug events during 30,397 person-years of observation (i.e., 50.1 adverse drug events per 1,000 person-years) (Gurwitz et al., 2003). And a study of 18 Massachusetts nursing homes identified 546 adverse drug events during 2,403 nursing home resident-years of observation (i.e., 227 adverse drug events per 1,000 resident-years) (Gurwitz et al., 2000).

Similarly, a major recent study found high levels of errors of omission in U.S. health care (McGlynn et al., 2003). More than 6,700 adults in 12 metropolitan areas were interviewed during the period 1998–2000 about selected health care experiences. In addition, those interviewed gave written consent for researchers to review their medical records and use the information to evaluate performance on 439 detailed clinical indicators of care for 30 acute and chronic conditions, as well as preventive care. The study focused on identifying instances in which proven, noncontroversial, poten-

TABLE 1-1 Health Care Errors in the United States

Type of Error

Inpatient Care

Other Care Settings


An estimated 44,000 to 98,000 hospitalized patients die annually in the United States (Institute of Medicine, 2000).

In outpatient care, 50 adverse drug events per 1,000 person-years were found (Gurwitz et al., 2003).

In nursing home care, 227 adverse drug events per 1,000 resident-years were found (Gurwitz et al., 2000).


Patients receive 55 percent of recommended care (McGlynn et al., 2003).

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