False Causation

What do horoscopes, psychic perceptions, and palm reading have in common? The Barnum effect, in which we falsely believe that certain statements are tailored especially for us, but in reality could apply to a general population.

A particularly interesting example of this surrounds lunar cycles, a myth that exists to this day. The lunar effect, as it’s known, is the belief that certain events occur more frequently when there is a full moon. Why do we believe this?

The answer is quite simple, but the pervasiveness of the myth speaks wonders of the workings of human perception.

The only reason people believe certain events coincide more often with a full moon is that a full moon is more likely to be noticed and remembered. This is supported by decades of research finding no such correlation with any event.

A crescent moon or new moon is unlikely to be remembered, as it has no significance attached to it, but a full moon has been a symbol of lore, mysticism, and superstition for centuries. It’s almost become a brand for occultist behaviour.

The lunar effect is classic confirmation bias. And it’s also a good example of a logical fallacy known as confusion of the inverse: where the likelihood of one thing happening is wrongly equated with the likelihood of its inverse happening.

Here it is applied to the lunar effect:

“I am likely to notice a full moon during [event],”

“Therefore, [event] is more likely to happen when there is a full moon.”

Substitute [event] for birth rates, aggressive behaviours, biological processes, or anything else commonly associated with a full moon, and the results are the same. The probability of one thing happening is not the same as the probability of its inverse. Therein lies the fallacy.

When two concepts are strongly associated with one another, the direction of causation can appear the same, even if research or common sense says otherwise. We most often assume false causations when we post-rationalise questionable behaviour.

This type of fallacy is harmless when applied to the relation between human behaviour and the moon, but can be dangerous in other contexts. Consider these political examples of ‘confusion of the inverse’:

“Most terrorists are Muslim,”

“Therefore, most Muslims are terrorists.”

“Autism occurs in children who have received vaccines,”

“Therefore, vaccines cause autism.

“Radicalists are likely to be religious,”

“Therefore, religious people are radicalists.”

Dangerous thinking, and it can fuel some very harmful behaviour. The lunar effect is only a fun myth, but the type of reasoning that leads to its belief is the same type of reasoning employed by many prejudiced people looking to justify their actions.

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