The danger of mixing up causality and correlation: Ionica Smeets at TEDxDelft

00:05:57
https://www.youtube.com/watch?v=8B271L3NtAw

Summary

TLDRThe speaker humorously warns of the common logical error of confusing correlation with causation, using several examples such as ice-cream sales being linked with drowning incidents. A graph might show that both are related, but the true cause is sunny weather that increases both swimming and ice-cream consumption. He then provides more examples, such as the false assumption that marriage extends men's lifespans, though healthier men are already more likely to marry, and the mistaken belief that children who sleep with lights on are more likely to become short-sighted, which ignores genetic predispositions. Another example showed good school performance as a cause of high self-esteem, rather than the reverse. The speech's goal is to teach the audience to critically assess claims of causality, ensuring a clear understanding of how and why one thing causes another, rather than relying solely on statistical correlations.

Takeaways

  • 🍦 Correlation doesn't imply causation, like with ice-cream sales and drowning rates tied to weather.
  • 💍 Marriage appears to extend life but healthier men marry; it's not causal.
  • 🔦 Sleeping with lights on was wrongly linked to short-sightedness; genetics is the true factor.
  • 📚 Good grades build self-esteem, not vice versa, as initially thought.
  • 🤔 Always question causal claims; correlation gives hints but doesn't prove causation.
  • 🔬 Understand 'why and how' for true causation, not just statistical links.
  • 😄 Use humor to illustrate logical fallacies, like ice-cream drowning example.
  • 👨‍👩‍👧‍👦 Be critical of assumptions in studies, especially those influencing lifestyle or parenting.
  • 🔍 Analyze if external factors influence both correlated elements.
  • 🧠 Think critically and avoid jumping to incorrect conclusions based on correlation.

Timeline

  • 00:00:00 - 00:05:57

    The speaker humorously suggests that ice-cream consumption leads to drownings, using a flawed correlation as evidence. The audience responds with laughter and applause after they explain the real underlying cause is likely good weather, which increases both swimming and ice-cream sales, not a causal link between ice-cream and drownings. The speaker uses this example to illustrate the common logical error of assuming causality from correlation and promises to provide more examples.

Mind Map

Video Q&A

  • What was the ice-cream example about?

    The speaker used the ice-cream example to illustrate a common logical error where increased ice-cream sales and drowning incidents are both correlated with nice weather, not with each other.

  • Why is marriage said to increase men's lifespan?

    Marriage is often misinterpreted as increasing lifespan, but it's actually healthier and wealthier men who tend to marry, leading to longer lifespans.

  • What discovery was made in the study about children sleeping with lights on?

    The study showed a correlation between sleeping with lights on and short-sightedness, which was later corrected to account for genetic factors related to parents.

  • How did self-esteem and school performance relate in the 1970s study?

    It was wrongly interpreted that high self-esteem leads to good grades, but later studies showed that good grades actually build self-esteem.

  • What is the main point of the speech?

    The main point is to highlight the mistake of confusing correlation with causation and to advise being skeptical of unsupported causal claims.

  • Why should we be cautious about causal claims?

    Causal claims need a clear explanation of how and why one thing causes another, not just correlation, which can be misleading.

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  • 00:00:00
    Transcriber: Emil-Lorant Cocian Reviewer: Ariana Bleau Lugo
  • 00:00:10
    Welcome. I came here today to warn you
  • 00:00:13
    about the dangers of ice-cream.
  • 00:00:15
    You may not be aware of this,
  • 00:00:16
    but these innocent looking cones full of sweetness
  • 00:00:20
    are one of the major causes of drownings.
  • 00:00:22
    And I've got the numbers to prove it.
  • 00:00:24
    So, if you plot a graph of the number of ice-creams that are sold,
  • 00:00:28
    and you compare it with the number of drownings,
  • 00:00:30
    you can see there is clearly an upwards trend,
  • 00:00:33
    and I think it's very safe to conclude from this
  • 00:00:36
    that we should ban ice-cream because it's very dangerous.
  • 00:00:39
    (Laughter) (Applause)
  • 00:00:44
    Since you're all smart people,
  • 00:00:46
    you've probably figured out
  • 00:00:47
    there's something wrong with my example.
  • 00:00:49
    What's really happening here is, of course,
  • 00:00:51
    that there is an underlying factor,
  • 00:00:53
    which is nice weather, you might have guessed it.
  • 00:00:56
    And if the weather is nice,
  • 00:00:57
    more people will go out swimming,
  • 00:00:59
    and unfortunately drown, and at the same time,
  • 00:01:02
    more people will buy ice-cream.
  • 00:01:04
    And it's not the ice-cream that's causing the drownings.
  • 00:01:07
    And here it's really easy to see that
  • 00:01:09
    there is something wrong,
  • 00:01:10
    but jumping to an incorrect conclusion about causality
  • 00:01:14
    when you see a correlation
  • 00:01:15
    is the most often made logical mistake.
  • 00:01:18
    And today my goal is to make sure that
  • 00:01:20
    in the future you can recognize this mistake.
  • 00:01:23
    And I really hope you can avoid making it
  • 00:01:25
    in the future for yourselves.
  • 00:01:27
    And I'll do this by just giving some famous examples.
  • 00:01:30
    And the first one is really rather innocent.
  • 00:01:33
    The fact is that
  • 00:01:34
    married men live longer than single men.
  • 00:01:38
    If you look at the statistics, you see that
  • 00:01:40
    this is really happening.
  • 00:01:42
    And women's magazines, they like to conclude from this
  • 00:01:44
    that marriage is very healthy for men,
  • 00:01:47
    because it makes them live longer.
  • 00:01:49
    Well, a friend of mine, he likes to joke that
  • 00:01:52
    marriage mainly makes life seem longer,
  • 00:01:55
    but -- (Laughter) --
  • 00:01:57
    that's because his wife is --
  • 00:02:00
    (Cheers) (Applause)
  • 00:02:03
    But so, can anyone guess what's going on here?
  • 00:02:06
    Because there is a causal relation,
  • 00:02:08
    but it's the other way around.
  • 00:02:11
    The fact is that men who are healthy,
  • 00:02:13
    and rich, and well educated,
  • 00:02:15
    and have a much higher life expectancy,
  • 00:02:18
    these are the men that are much more likely
  • 00:02:19
    to find a wife -- that's the way women are --
  • 00:02:22
    and the guys who have a very low life expectancy,
  • 00:02:25
    so they're unhealthy and poor,
  • 00:02:27
    they are not as likely to get married.
  • 00:02:29
    So it's the high life expectancy
  • 00:02:31
    that is causing the marriage,
  • 00:02:33
    not the other way around.
  • 00:02:35
    Well, and this, of course, you know,
  • 00:02:37
    it's not so serious, no one will get married
  • 00:02:38
    just because he read this.
  • 00:02:40
    So let's move to a more serious example.
  • 00:02:43
    It was also more serious research.
  • 00:02:45
    In Nature there was a study in 1999 that showed
  • 00:02:49
    that young kids who sleep with the lights on,
  • 00:02:52
    that they have a much higher probability
  • 00:02:54
    of becoming short-sighted later in life.
  • 00:02:56
    But the researchers, they were smart,
  • 00:02:58
    and they wrote very careful
  • 00:03:00
    that they had found a correlation,
  • 00:03:03
    and they didn't know how the causal relation might work,
  • 00:03:06
    but just to be sure they advised all parents
  • 00:03:08
    to turn off the lights at night.
  • 00:03:11
    And in the popular media this became that
  • 00:03:13
    bed lamps were night abuse, children's abuse,
  • 00:03:16
    and that it was very bad
  • 00:03:17
    if parents used lamps in the bedroom.
  • 00:03:20
    And many parents were worried.
  • 00:03:22
    I can imagine, if this would have happened
  • 00:03:23
    when my son was sleeping with the lights on,
  • 00:03:25
    I would had felt really bad.
  • 00:03:26
    But luckily, the article had to be corrected
  • 00:03:30
    the next week, and maybe some of you can guess,
  • 00:03:34
    and if there are biologists in the audience, they know.
  • 00:03:37
    Short-sightedness is genetic.
  • 00:03:40
    And so, it's parents who are short-sighted.
  • 00:03:42
    And those are the parents who like to
  • 00:03:43
    leave the light on in the bedroom,
  • 00:03:45
    and they also are the parents
  • 00:03:47
    who have short-sighted kids.
  • 00:03:49
    So again, a simple mistake, easy to make.
  • 00:03:53
    Then, what is I think the worst example I know --
  • 00:03:56
    I know many of them,
  • 00:03:57
    I see at least one of these
  • 00:03:58
    in the newspapers every week.
  • 00:04:00
    But this is a classic one: in the '70s,
  • 00:04:02
    researchers found that there is a very strong link
  • 00:04:05
    between kids who do well in school, get good grades,
  • 00:04:08
    and kids who have a high self-esteem.
  • 00:04:11
    And they concluded from this
  • 00:04:12
    that it's very important to make sure that
  • 00:04:14
    young kids are, you know, raised
  • 00:04:17
    to be confident and proud of themselves,
  • 00:04:19
    because if their self-esteem is high,
  • 00:04:21
    the good results will follow.
  • 00:04:23
    And this forethought was told to parents,
  • 00:04:25
    especially in the US, for generations,
  • 00:04:28
    that just make sure that your kid is proud and confident,
  • 00:04:31
    then all will turn out well.
  • 00:04:33
    And many years later, someone did another study
  • 00:04:36
    just to see in which
  • 00:04:38
    direction the cause was working.
  • 00:04:40
    And they found that it was in the opposite direction.
  • 00:04:43
    So the good grades were causing the self-esteem,
  • 00:04:46
    and self-esteem wasn't causing good grades.
  • 00:04:49
    And it was even worse.
  • 00:04:51
    So kids who are raised just to have high self-confidence,
  • 00:04:55
    and not excel at anything --
  • 00:04:56
    it can be sports or music,
  • 00:04:58
    doesn't have to be school --
  • 00:04:59
    the kids who are just proud of themselves,
  • 00:05:01
    and then fail at everything,
  • 00:05:03
    in the end they will have a very low self-esteem,
  • 00:05:05
    and not be able to make anything of their life.
  • 00:05:08
    So this was a very serious correlation mistake.
  • 00:05:11
    And what I want for today is for you
  • 00:05:14
    to remember that the next time
  • 00:05:15
    someone wants to prove that there is a causal relation
  • 00:05:18
    between something and something else --
  • 00:05:20
    it can be anything, it can be vaccines and autism,
  • 00:05:23
    it can be female bankers and the financial crisis,
  • 00:05:27
    and if they -- (Laughter) -- point out to you
  • 00:05:29
    that there is a very strong relation,
  • 00:05:31
    remember that it's not enough to have a correlation.
  • 00:05:34
    It gives a very good hint of what might be happening,
  • 00:05:37
    but before you can conclude that one thing causes something else,
  • 00:05:40
    you need to know why it does and how it does.
  • 00:05:43
    So, when in doubt, just remember the ice-cream.
  • 00:05:46
    Thank you very much.
  • 00:05:48
    (Applause)
Tags
  • correlation
  • causation
  • logical fallacies
  • ice-cream
  • drowning
  • marriage
  • self-esteem
  • statistics
  • genetics
  • critical thinking