Eating at McDonald’s Gives you Acne

That is a libelous statement, but it is fairly obviously true, I was in McDonald’s with my children only last weekend and it was jam-packed full of spotty teenagers.

It is a slam-dunk case of cause and effect.  All those burgers will make you spotty.

Really?  What else could be going on?

If you are a McDonald’s in-house lawyer, please don’t sue, clearly I am talking rubbish.  It isn’t the Big Mac that’s causing the spots, it is simply that the youthful clientele at McDonald’s are more likely to have spots than people of my advancing years.

I am jumping to conclusions.  Correlation is not the same as causation.

Now a trickier, more controversial statement…

Single sex schools provide a better education

This is a topic close to my heart.  I send my daughters to a girls only school.  The grades are great.  Now obviously that is because a single sex education is the best education.

Really?  What else could be going on?

Is there anything else that could be causing the good grades?

The school I send my children to is selective, they only accept clever children (now is not the time to start debating their paternity).

The school I send my children to is also a fee paying school.  You have to earn a reasonable amount to foot the bill.   Rightly or wrongly clever people tend to earn more, and clever people have clever children.

So what is the real cause of the better grades?

  • The selection of children?
  • The brighter parents?
  • The single sex education?

Correlation is not the same as causation.

Now for something shockingly controversial…

The MMR vaccination causes autism

Fortunately that belief has now been conclusively debunked, but not until thousands of people had put their children at risk of catching measles, mumps or rubella.

Correlation isn’t the same as causation

Unfortunately the more plausible a theory sounds and the less we know about a subject the more likely we are to believe the relationship.

So before you jump to conclusions and solutions ask yourself…

Really?  What else could be going on?

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Correlation isn't causation

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Images by DennisSylvesterHurd and Svadilfari




  1. James,

    Confusing correlation with causation is one of my pet hates too and you’ve articulated the problem very well. But I have come to learn that there is any area of life which is an exception to your principle and where this is permissible.

    It’s when compelling statistics are used in politics to justify action (or, this week, inaction).

    Different rules must apply in politics, because politicians do this all the time. And surely they are intelligent people who wouldn’t make that kind of mistake?

  2. Hello James,

    Correlation is not causation from a statistical perspective. From a human perspective correlation IS causation. This way of being-in-the-world is so automatic that we don’t notice it. Let me correct that, we especially don’t notice it when it really matters that we do notice it.

    Take the MMR jab, this was a high stakes emotional issue. As a father/mother do you believe the government or do you believe an ‘independent doctor’ given that you do not have access to the scientific research and are probably not in a position to evaluate it? Why would any sane person believe anyone from Government? We ‘know’ that Government lies, spins, deceives, misrepresents. We ‘know’ that doctors are more ethical and we especially ‘know’ this because we want to ‘know’ that they are ethical – as our lives are in their hands from time to time. So you have parents making the choice that they did.

    How much of our way of life would fall apart if we really, truly, practiced correlation is not causation. Take the world of business, are Tops really the cause of stellar business performance? Or is this simply correlations masquerading as causation working alongside a selective memory where we focus only on the successes and discard failures? Or is it that in a game where many are experimenting some, simply by luck, select an option tha ends up working? And then they get rewarded for simply experimenting and being lucky?

    All the best

    • James Lawther says:

      Thanks for your comments Maz, I couldn’t agree more.

      The question in my mind is “Can I influence that?”


    • Hi Maz, James,
      “Lies, damn lies and statistics” as one politician (Disraeli) once said. Hmm I wonder if I believe him ;)

      However, Maz you go on to say “We ‘know’ that doctors are more ethical and we especially ‘know’ this because we want to ‘know’ that they are ethical – as our lives are in their hands from time to time.”

      I’d like to ask… we really ‘know’ that doctors are more ethical especially given all of the hospital scandals that have emerged recently? Or, is it that we want to believe that they are more ethical because our lives and the lives of others could be in their hands?


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