Reading this short article about the value of health data to combat unfounded best practices reminded me of another story from How Doctors Think:
One of the most common congenital abnormalities of the heart is a hole between the two upper chambers, between the right atrium and the left atrium. Since the pressure in the left side of the heart is higher than in the right, blood will flow from the left atrium through the hole into the right atrium. This aberrant blood flow is called a shunt and can overload the right side of the heart, leading to heart failure and other complications. Lock told me that doctors send children for surgery to close these holes if there is a two-to-one shunt, meaning that twice as much blood flows through the right side of the heart than the left.
“Do you know where that two-to-one number came from?” [Dr. James] Lock [, chief of cardiology at Boston's Children's Hospital,] asked. I imagined ti was from careful clinical studies of children with the hold. “You would think so. But you’d be wrong. At a medical meeting in the 1960s, a pediatrician presented the question ‘When should the hold be closed?’ to a group of cardiologists. There was a heated debate about how much shunting required a surgical fix. So the meeting organizers, out of desperation, took a vote. Some voted for a lower number, some for a higher number. The median ended up being two-to-one. This was published in the American Journal of Cardiology. So now all textbooks have as the truth that you should close a hole when the shunt is two-to-one.
In reality, Children with a two-to-one shunt can live a healthy life without ever requiring treatment. Heart surgery, as one can imagine, is always a dangerous proposition that carries risks for the patients.