Physicians tend to have unrealistic expectations of the success of multi-step medical procedures

Whether a woman is giving birth or a man is undergoing a cancer biopsy, medical care is rarely straightforward. An unexpected complication can occur at any time, especially during treatments that require multiple steps.

Still, doctors tend to have unrealistic expectations of the success of multi-step medical procedures, according to a new nationwide study conducted by scientists at the University of Utah Health and their collaborators. They say inflated estimates of success can adversely affect treatment decisions and lead to unintended harm to patients.

Overall, nearly 8 out of 10 physicians surveyed believed that the odds of achieving a desired outcome after a medical procedure were greater than the success of one or more steps leading to that outcome.

The study, which appears in JAMA network opened, [DD1] points to a serious logical division between physicians who fail to consider that each step in the process has its own risks that can reduce the likelihood of success for the desired medical outcome, according to Scott Aberegg, MD, an intensive care pulmonologist at U of U Health .

All too often, doctors pretend that the stars align more often than they actually do. They tend to focus on the desired outcome rather than the actual chances of success involved in each intermediate step. That way we can’t keep making medical decisions. We have to base them on more realistic expectations.”

Scott Aberegg, MD, intensive care pulmonologist, U of U Health

The study, conducted by Aberegg; Hal Arkes, Ph.D., of Ohio State University; and Kevin Arpin, Ph.D., a forensic specialist at Travelers Insurance Company in Connecticut, tried to determine how common a phenomenon called conjunction fallacy is in medicine.

Conjunction fallacy occurs when a person believes that a combination of events or statements is more likely than any of its individual components.

For example, suppose a doctor notices skin growth on a patient and 80% suspect it to be cancer. There is also an 80% chance that the pathologist will see cancer on a lab biopsy. The wrong assumption – the conjunction fallacy – would be that there is more than an 80% chance that the pathologist will see cancer on the patient’s biopsy sample.

In reality, the chance that the pathologist will see cancer on this patient’s biopsy is 64% because the patient first to have cancer and then the pathologist has to see it on the biopsy.

“A lot of doctors are just not good at calculating probability,” Aberegg says. “As a result, they often miss opportunities to make better treatment decisions.”

In their study, Aberegg and colleagues asked 215 obstetricians and pulmonologists to evaluate scenarios they might encounter while caring for patients.

For example, in one scenario, midwives were confronted with a 29-year-old pregnant woman who was in labor. However, the child is not well positioned for a vaginal delivery. In this case, the doctors were asked to estimate the likelihood that the child would be in a deliverable position and be born without the need for a cesarean section.

Overall, 78% of physicians evaluating one of the three scenarios in the study estimated that the probability of the desired outcome would be greater than the probability of the two separate events required for it to occur. This is a mathematical impossibility, Aberegg says.

“Our research shows that if you underestimate the probability that two events will have to happen to get the desired outcome, you can put your patients at risk unnecessarily,” Aberegg says. “In the case of the delivery scenario, you could wait a long time for that baby and end up having to do a cesarean section anyway. That delay can be harmful to both mother and child.”

All physicians participating in the studies had an average of 25 years of experience. Yet this expertise did not appear to prevent them from opting for the conjunction fallacies presented in the study. This isn’t all that surprising, however, given that previous research has shown that nearly 50% of medical students are prone to these types of probability errors, according to Aberegg.

“There are tremendous opportunities in medical education to improve the curriculum in terms of teaching the importance of probability in medical settings,” Aberegg says. “Numbers are the most reliable source of right decisions in medicine.”

Aberegg urges practicing physicians not only to rely on their experience, but to do their best to stay current with the latest probability research published in medical journals on various conditions and procedures.

One of the study’s limitations is that participants were asked to provide written answers that could have been different if they had cared for real patients.

However, Aberegg believes the research could have broad implications.

“Our results are very strong,” Aberegg says. “We believe they represent a common phenomenon in medicine. I am interested in cataloging more examples further so that the full breadth of this potential problem can be uncovered and hopefully resolved.”


Reference magazine:

Arkes, HR, et al. (2022) Analysis of physicians’ probability estimates of a medical outcome based on a series of events. JAMA network opened.

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