Uncommon Common Sense

By Bill Frayer

It’s Easy to Identify a False Cause

correlation vs causation


So here’s the problem. You hear a report on television that a new study has found that people who take a daily multivitamin live longer than people who do not. “Wow,” You exclaim, “I better start taking a multivitamin” Simple, right? Well, not so fast.

As a good thinker, you decide to read a description of the actual study, and you find, as expected, that the study asked people to report if they took a multivitamin every day, and followed them for a period of time. They eventually looked at the data and discovered that the vitamin takers lived longer. In other words, taking a vitamin correlated with a longer life.

The problem is, it is impossible to tell if the vitamins actually caused the long life. It’s likely that people who take vitamins practice other healthy habits. Maybe they are more likely to exercise, eat good food, and drink the recommended glass of red wine each day. So we don’t know what, exactly, caused the extension of life. We can derive an important axiom from this example: correlation is not causation. If two events occur together (correlation) we cannot assume that the first event caused the second event (causation).

Take superstitions as an example. Let’s consider a baseball player who is in a batting slump, and one day forgets to shave and gets three hits. He may (incorrectly) conclude that the growth on his face allowed him to hit better. In any event, he is unlikely to shave the next day. If his batting continues to improve, he may grow a beard. At some point we might suggest that the beard increases his confidence, thus his performance. But at its heart, this is a false cause fallacy.

This fallacy is also known by its Latin name, post hoc, ergo propter hoc, which literally means, after this therefore because of this. This is such a common thinking error, that we are all guilty of making it at one time or another. It is appealing precisely because it’s so simple. It’s easy to see what looks like the most obvious cause, an oversimplification error.

Think of some examples from your own life. Here are a few from mine:

I was quick to blame one of my children’s friends for my child’s undesirable behavior. It may have contributed to it, but that was not the entire story. I wore my lucky Red Sox shirt during the 2004 ACLS and World Series. Of course the Red Sox won, but it logically had little to do with my shirt. And finally, I used to take antioxidant vitamins because there were numerous reports that foods rich in these antioxidants was correlated with lower rates of cancer and heart disease. Finally, clinical research demonstrated that taking the antioxidant in pill form did not have the same protective effect, and that some supplements could actually be dangerous.

People tend to make this error because it’s easy and makes them feel as though they have some control over their lives. After all, if you can assure a safe plane ride by drinking cranberry juice before you leave, why not? If it worked before, it should keep working, right? Simple answers make us feel secure, but they easily delude us. The causes of events are usually the result of many factors, over which we may have little or no control. Sad but true.

Bill Frayer




Column: Uncommon Common Sense




Bill Frayer lived all of his adult life in Maine until moving to Mexico in 2007.  He had a long career teaching writing, critical thinking, and communication at the community college and university level.  He has published a critical thinking textbook and four volumes of poetry.  Stirring up trouble with his column for the last eight years, he enjoys hearing from those who have strong opinions about what he writes.  Now a snowbird back in Maine, he enjoys playing blues, eating lobster, and fishing with his granddaughter.  In Ajijic he enjoys leading TED talks at LCS and talking poetry with his fellow poets.



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