Add diagnostic error in the emergency room and walk-in clinics to error in the out-patient offices of medicine and you have more than 200 million errors.

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Often, a diagnosis "evolves over time" so a patient's problem might not be clear from initial symptoms, Dr Singh says, but that isn't necessarily a diagnostic error.

WSJ: Adding Up Diagnosis Errors

Right now, diagnostic error for human doctors is 45 percent.

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DeBakey VA Medical Center, Houston, Texas and assistant professor of medicine at Baylor College of Medicine who has wrote several studies on diagnostic error, says that while the Hopkins study confirms previous research, malpractice data provide a limited picture.

WSJ: Adding Up Diagnosis Errors

"There isn't going to be one magic bullet to solve the problem of diagnostic error, but we can start by consistently monitoring and measuring it, " says David Newman-Toker, lead author of the study and an associate professor of neurology at Hopkins.

WSJ: Adding Up Diagnosis Errors

Diagnostic and patient management error caused by cognitive mistakes in the exam room are all too often overlooked and unmentioned in the discussion of repairing our broken healthcare system.

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