How many deaths are due to medical error? Getting the number right

The Institute of Medicine (IOM) report on medical errors created an intense public response by stating that between 44,000 and 98,000 hospitalized Americans die each year as a result of preventable medical errors.

To determine how well the IOM committee documented its estimates and how valid they were.

We reviewed the studies cited in the IOM committee's report and related published articles.

The two studies cited by the IOM committee substantiate its statement that adverse events occur in 2.9% to 3.7% of hospital admissions. Supporting data for the assertion that about half of these adverse events are preventable are less clear. In fact, the original studies cited did not define preventable adverse events, and the reliability of subjective judgments about preventability was not formally assessed. The committee's estimate of the number of preventable deaths due to medical errors is least substantiated. The methods used to estimate the upper bound of the estimate (98,000 preventable deaths) were highly subjective, and their reliability and reproducibility are unknown, as are the methods used to estimate the lower bound (44,000 deaths).

Using the published literature, we could not confirm the Institute of Medicine's reported number of deaths due to medical errors. Due to the potential impact of this number on policy, it is unfortunate that the IOM's estimate is not well substantiated.