Why You Shouldn’t Believe in the Stork

The Art of Thinking Clearly - Rolf Dobelli 2014

Why You Shouldn’t Believe in the Stork

False Causality

For the inhabitants of the Hebrides, a chain of islands north of Scotland, head lice were a part of life. If the lice left their host, he became sick and feverish. Therefore, to dispel the fever, sick people had lice put in their hair intentionally. There was a method to their madness: As soon as the lice had settled in again, the patient improved.

In one city, a study revealed that in each blaze, the more firefighters called out to fight it, the greater the fire damage. The mayor imposed an immediate hiring freeze and cut the firefighting budget.

Both stories come from German physics professors Hans-Peter Beck-Bornholdt and Hans-Hermann Dubben. In their book (unfortunately there is no English version), they illustrate the muddling of cause and effect. If the lice leave the invalid, it is because he has a fever and they simply get hot feet. When the fever breaks, they return. And the bigger the blaze, the more firefighters were called out—not, of course, vice versa.

We may smirk at these stories, but false causality leads us astray practically every day. Consider the headline: “Employee Motivation Leads to Higher Corporate Profits.” Does it? Maybe people are simply more motivated because the company is doing well. Another headline touts that the more women on a corporate board, the more profitable the firm is. But is that really how it works? Or do highly profitable firms simply tend to recruit more women to their boards? Business book authors and consultants often operate with similar false—or at least fuzzy—causalities.

In the ’90s, there was no one holier than the then-head of the Federal Reserve, Alan Greenspan. His obscure remarks gave monetary policy the aura of a secret science that kept the country on the secure path of prosperity. Politicians, journalists, and business leaders idolized Greenspan. Today we know that these commentators fell victim to false causality. America’s symbiosis with China, the globe’s low-cost producer and eager buyer of U.S. debt, played a much more important role. In other words, Greenspan was simply lucky that the economy did so well during his tenure.

A further example: Scientists found that long periods in the hospital affected patients adversely. This was music to health insurers’ ears, who, of course, are keen to make stays as brief as possible. But, clearly, patients who are discharged immediately are healthier than those who must stay on for treatment. This hardly makes long stays detrimental.

Or, take this headline: “Fact: Women Who Use Shampoo XYZ Every Day Have Stronger Hair.” Though the context can be substantiated scientifically, this statement says very little—least of all, that the shampoo makes your hair stronger. It might simply be the other way round: Women with strong hair tend to use shampoo XYZ—and perhaps that’s because it says “especially for thick hair” on the bottle.

Recently I read that students get better grades at school if their homes contain a lot of books. This study was surely a shot in the arm for booksellers, but it is another fine example of false causality. The simple truth is that educated parents tend to value their children’s education more than uneducated ones do. Plus, educated parents often have more books at home. In short, a dust-covered copy of War and Peace alone isn’t going to influence anyone’s grades; what counts is parents’ education levels, as well as their genes.

The best example of false causality was the supposed relationship between the birth rate and the numbers of stork pairs in Germany. Both were in decline, and if you plot them on a graph, the two lines of development from 1965 to 1987 appeared almost identical. Does this mean the stork actually does bring babies? Obviously not, since this was a purely coincidental correlation.

In conclusion: Correlation is not causality. Take a closer look at linked events: Sometimes what is presented as the cause turns out to be the effect, and vice versa. And sometimes there is no link at all—just like with the storks and babies.