Correlation does not imply causation” is a well-worn phrase, an expression used to explain things, and (often) to smugly shut down an argument. There’s a meta effect in which the phrase has some causal power: it can cause an argument to be discarded.

Of course, though, correlation often does imply causation. Cause and effect are most definitely correlated. Pearson even designed his correlation coefficient as an index of the strength of causation. It’s just that correlation is not enough to allow a valid causal inference to be made.

Causality and the Cat

Peppermint, our cat, looking smug after she’s woken me up in the morning.

Every morning at around 5:00am, without fail, she carries out a complicated routine in my bedroom. She starts by meowing loudly and then begins picking at the door to the closet. This reverberates loudly, enough to wake me. She will rattle the window blinds and sometimes open and slam the door to the room, and then start picking at that door. These are all loud enough, and unrelenting enough to cause me to get up, at 5:30, and head downstairs where I feed her. And today, she might have even caused me to write this essay.

These events, picking at the door and me getting up, are highly correlated. But are they causally linked? I like to imagine the cat thinks they are. That somewhere in the recesses of her dusty little cat-mind, she believes that she and she alone caused me to get up and feed her. This, I believe anthropomorphically, causes a sense of independent agency in the cat. She has purpose. She has power. Certainly, there is strong behavioural association and that’s why she continues to engage in the behaviour.

What is the candidate for causality?

So the question I asked this morning was: Did she cause me to wake up or did she simply contribute to a larger causal model?

Or, did I actually cause her behaviours by getting up and reinforcing her actions, thus establishing and contributing to the symphony of slamming, picking, and pestering that seems like the cause but is actually the effect of my early rising habit? There really is no simple answer.

We are all creatures of habit

Like my cat, we too are creatures of habit. We have a habit to look for causality in the world. These tendencies are reinforced by the correlations we observe. And because of that, we can’t stop from believing in causes that are correlated and easy to observe.

Originally published at jpminda.com on December 27, 2018.

Author and Professor of Psychology at Western University. I write about Cognitive Science, Psychology, and Higher Education. http://jpminda.com/

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