Errors in Clinical Reasoning

Physicians make diagnostic and therapeutic decisions at every moment in their daily lives. Quality of care and patient outcomes, including sometimes distinction between life and death, come out of such decisions. In most cases, physicians' judgments are correct, but of course, they also fail. Errors, in fact, occur in medicine, and the Institute of Medicine's well-known report To Err Is Human recently called the public's and professionals' attention to this reality. Since then, the frequency and impact of adverse patient effects provoked by medical errors have been increasingly recognized. In the United States, it is estimated that medical errors result in 44,000 to 98,000 unnecessary deaths and around 1 million injuries each year. Even considering the lower estimate, deaths due to adverse events resulting from medical errors exceed the deaths attributable to motor vehicle accidents, breast cancer, or AIDS. Similar phenomena have been reported by studies in other countries. In Australia, for instance, medical errors are estimated to result in as many as 18,000 deaths, and more than 50,000 patients become disabled each year.

Medical errors occur in a variety of healthcare settings and in different stages of care. They may arise due to drug misuse or failures during the therapeutic phase, for instance, but due to their frequency and impact, diagnostic errors have received growing attention. Diagnostic error may be defined as a diagnosis that was unintentionally delayed (sufficient information for establishing the diagnosis was available earlier), incorrect (another diagnosis was made before the correct one), or missed (no diagnosis was ever made), as judged from the analysis of more definitive information. When a diagnosis is incorrect or does not entirely address the patient's problem, treatment can be delayed and/or wrong, sometimes with devastating consequences for patients and healthcare providers. Diagnostic mistakes represent a substantial and costly proportion of all medical errors. In the Harvard Medical Practice Study, the benchmark for estimating the amount of injuries occurring in hospitals, diagnostic errors represented the second largest cause of adverse events. In a recent study of autopsy, diagnostic discrepancies were found in 20% of the cases, and in half of them, knowing the correct diagnosis would have changed the case management. Indeed, postmortem studies indicate that the rates of diagnostic errors with negative impact on patient outcomes hover around 10%; this rate is stable across hospitals and countries and has not been affected by the introduction of new diagnostic technologies.

Undoubtedly, not all diagnostic errors can be attributed to faults in physicians' clinical reasoning. In a typology of medical errors that has been frequently used by Mark Graber and other authors, the so-called system-related errors come out from latent flaws [Page 451]in the health system that affect physicians' performance. This type of error derives from external interference and inadequate policies that affect patient care; poor coordination between care providers; inadequate communication and supervision; and factors that deteriorate working conditions, such as sleep deprivation and excessive workload. In a second category of errors, referred to as no-fault errors, the correct diagnosis could hardly be expected due to, for example, a silent illness or a disease with atypical presentation. However, a third category of errors, namely, cognitive errors, occur when a diagnosis is missed due to incomplete knowledge, faulty data gathering or interpretation, flawed reasoning, or faulty verification. As arriving at a diagnosis depends largely on a physician's reasoning, cognitive faults play an important role, particularly in diagnostic errors. Indeed, a recent study in large academic hospitals in the United States found that cognitive factors contributed to 74% of the diagnostic errors in internal medicine.

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