Simplifying Skepticism: Correlation vs Causation

23 Dec
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by Benjamen Johnson

A few days ago I pondered:

…how am I going to relate concepts like confirmation bias or correlation versus causation to my children? They’ll be lucky if formal schooling will introduce them to these concepts before college (even then it’s iffy). I think the seven year old mind can grasp these concepts if they are explained properly and the sooner they learn them the less baggage they will have to throw away when they do embrace them.

To address this issue, I started by giving a simple analogy of anomaly hunting that related it to a jigsaw puzzle. Continuing on that track, today I thought I’d present one of the best (and most entertaining) examples on TV about the correlation equals causation fallacy.

First a bit of background: Ned Flanders panics because he sees a bear on the street. So the whole town overreacts and demands the city to do something about it. They over-respond to the townspeople’s concerns in classic fashion by creating the Bear Patrol. The scene starts with homer outside proudly watching the bear patrol canvas the city.

Homer: Not a bear in sight. The Bear Patrol must be working like a charm.
Lisa: That’s spacious[sic] reasoning, Dad.
Homer: Thank you, dear.
Lisa: By your logic I could claim that this rock keeps tigers away.
Homer: Oh, how does it work?
Lisa: It doesn’t work.
Homer: Uh-huh.
Lisa: It’s just a stupid rock.
Homer: Uh-huh.
Lisa: But I don’t see any tigers around, do you?
[Homer thinks of this, then pulls out some money]
Homer: Lisa, I want to buy your rock.
[Lisa refuses at first, then takes the exchange]

— Quoted from the Simpsons Archive [Much Apu About Nothing]

I don’t think I could come up with a better example and I’m not the only person who’s used this to demonstrate that correlation doesn’t imply causation. uses it as an example in a course on critical thinking: The Unofficial Guide to OCR A-Level Critical Thinking.

I think I’m going to watch this episode this afternoon with my kids.

3 Responses to “Simplifying Skepticism: Correlation vs Causation”


  1. Reading Digest: Roasting on an Open Fire Edition « Dead Homer Society - December 30, 2011

    […] Simplifying Skepticism: Correlation vs Causation – Illustrating correlation and causation with tigers, rocks and the Bear Patrol. […]

  2. Lisa Simpson Gets Why Correlation Does Not Imply Causation | Get Elastic Ecommerce Blog - September 17, 2012

    […] you can’t learn critical thinking from TV?I’m passing along this perfect example (via here and here) of why “correlation does not imply causation.”In the Simpson’s episode […]

  3. Why Does More Education Increase Income? | A Little Bit of Everything - December 17, 2012

    […] with causation, the notion that umbrellas cause rain or diet soda causes weight gain or even that a rock keeps away tigers.  In a professional setting, I’ve seen this confusion lead companies to mistakenly justify […]

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