The Semmelweis Reflex

Logic, data, and an open mind can help us avoid falling victim to this bias

It's easy to reject information because we assume it to be false; it is far more difficult, but very worthwhile, to fully consider the validity of "other" information that may ultimately prove to be true, upsetting long-held convictions. Fei Meng

Ignaz Semmelweis (1818–1865) is hardly a household name, but it should be.

In 1844, the young Hungarian physician was assigned to an obstetrics hospital in Vienna, where puerperal fever, described today as postpartum infection, was rampant among mothers who had delivered babies. In one clinic, Semmelweis noticed that the death rate among these mothers was about 20 percent, while in another facility the rate was about one third of that percentage. The only difference between the two clinics was that the first was serviced by medical students, who often came straight from the dissection table, while the second clinic was a training ground for midwives.

Deducing that the medical students were in some way carrying infection to the mothers, Semmelweis hit on the idea of having them wash their hands in a mixture of chlorinated lime, and the death rate quickly plummeted. Though he spent years afterward promoting this idea—several hospitals adopted the practice, with stunningly positive results—the medical authorities in general scoffed at his findings and rejected his teachings. Authority and tradition crushed both Semmelweis, who died after a short stay in an insane asylum, and his discovery.

From his tragic history came the modern term Semmelweis Reflex bias, describing the tendency to reject a piece of information that demonstrates that something we believe is wrong. Whether subconsciously or deliberately, when we turn our back on facts and data that prove that we are in error, we have surrendered to this bias.

This is not an uncommon occurrence. In the 1920s, for example, U.S. Army Gen. Billy Mitchell offered proof that aircraft had rendered battleships obsolete in naval warfare. His criticism of the upper echelons of command for ignoring this premise led to a conviction of insubordination, and Mitchell resigned from the service. By the end of World War II, however, battleships were becoming obsolete, and aircraft had become the key to victory in naval engagements.

We’ve seen similar examples of the Semmelweis Reflex in our own times. During the COVID-19 pandemic, for example, some scientists and physicians who had devised effective ways to fight the virus were silenced by the establishment and banned from social media. Authority trumped valid innovation.

In our own lives, this bias also can come into play. We become accustomed to a certain way of thinking or doing things, and are loath to change. A supervisor assigned to make a shipping department more efficient meets resistance from longtime employees. Two friends who are polar opposites in politics discuss some hot topic of the day, and though one of them cites a wealth of data and facts to support his point, the other refuses to concede. A financially strapped couple sit down to discuss their summer budget, but the husband adamantly resists giving up the week renting a house with friends at the Outer Banks. “We’ve always done it this way,” he says. “What would they think of us?”

To avoid falling into this rut, imitate the same procedures employed by Semmelweis. When you notice that some long-accepted way of thinking or acting may be wrongheaded, consider the facts and data, then experiment to discern if this new way does indeed work better. If the experiment succeeds, make a change. If it fails, return to your time-tested path.

Writer Somerset Maugham once noted, “Tradition is a guide and not a jailer.” With tradition as our guide, but with common sense and logic as our companions, we can avoid the Semmelweis Reflex.