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In some islands north of Scotland, head lice, which live on the hair or skin of people or animals, were a part of life. If the lice left their host, he became sick and feverish. Therefore, 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. The story explains the confusion of cause and effect. If the lice leave the sick, it is because he has a fever and they simply get hot feet. When the fever breaks, they return. We may laugh at this story, but false causality misleads us practically every day.

Consider the headline: “Fact: Women Who Use Shampoo XYZ Every Day Have Stronger Hair.” 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.

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

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 also an example of false causality. This 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.

Another example of false causality was the supposed relationship between the birth rate and the numbers of stork (鹳) 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 the same. Does this mean the stork actually does bring babies? Obviously not, since this was a purely accidental connection.

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