Researchers analyze “conjunction fallacy” and find need for realistic expectations.
Patients could face unnecessary risks when physicians overestimate probabilities of success for medical procedures that require more than one step.
A study analyzed physicians’ ability to calculate probability and found they “consistently overestimated the combined probability of two events compared with the probability calculated from their own estimates of the individual events.” The phenomenon is called conjunction fallacy, when a person believes that a combination of events or statements is more likely than any one of its individual components.
“All too often, doctors act as though the stars align more frequently than they actually do,” coauthor Scott Aberegg, MD, said in a news release. “They tend to focus on the desired outcome rather than the actual chances of success involved in each intermediary step. We can’t continue making medical decisions that way. We need to base them on more realistic expectations.”
Aberegg, a critical care pulmonologist at University of Utah Health, conducted the study with Hal Arkes, PhD, of The Ohio State University; and Kevin Arpin, PhD, a forensic specialist at Travelers Insurance company in Connecticut.
They surveyed 215 obstetricians and pulmonologists about example scenarios they might encounter, such as a 29-year-old woman delivering a child not positioned properly for vaginal birth, or a physician discovering a patient has a pulmonary nodule.
Participants were asked about the likelihood of success for treatment scenarios and 78.1% of physicians committed the conjunction fallacy, resulting in substantial overestimation of probability of two-step sequences, according to the study.
A general explanation could be that “many physicians may not be facile in the calculation of probability or even basic numeracy,” the study said, but the medical consequences may be substantial. For example, overestimating the probability of the presence of a cancerous nodule and the ability to detect cancer through biopsy could lead to unnecessary confusion for patients and physicians, or selecting suboptimal diagnostic strategy, the authors said.
In the case of a delivery, the fallacy could result “in catastrophic maternal and/or fetal consequences,” said the study, which was inspired by a real case of medical tragedy.
“In that case, patient counseling related to probabilities was misguided in a way consistent with the conjunction fallacy, resulting in the loss of a child due to injuries sustained during prolonged labor,” the study said.
“Our study shows that if you poorly estimate the probability of two events needing to happen to get the result you desire, then you could be putting your patients at unnecessary risk,” Aberegg said in the news release. “In the case of the childbirth scenario, you could end up waiting around for a long time for that baby and end up having to do a C-section anyway. That delay could be harmful for both mother and child.”
The study, “Analysis of Physicians’ Probability Estimates of a Medical Outcome Based on a Sequence of Events,” was published in JAMA Network Open.