Correlation and Causation

Some people think vaccines are associated autism simply because we are giving more vaccines and protecting kids against more vaccine-preventable diseases, just as more kids were getting diagnosed with autism.

So it has to be the vaccines!

Correlation implies causation, right?

Not really.

The saying is “correlation does not imply causation.”

Nate Silver explains it very well:

“Most of you will have heard the maxim “correlation does not imply causation.” Just because two variables have a statistical relationship with each other does not mean that one is responsible for the other. For instance, ice cream sales and forest fires are correlated because both occur more often in the summer heat. But there is no causation; you don’t light a patch of the Montana brush on fire when you buy a pint of Haagan-Dazs.”

Correlation does not imply causation.

Just because two things happen at the same time, it doesn’t mean that one caused the other.

Correlation does not imply causation.
Correlation does not imply causation.

And just because we don’t know what causes autism, it doesn’t mean that it is vaccines. That is especially true since so many studies have shown that it is not vaccines.

But, and this is what confuses a lot of people, sometimes correlation does show causation.

When?

When the evidence supports the correlation!

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2 thoughts on “Correlation and Causation

  1. There is a 0.97 correlation between autism rates and the Federal Debt. By that logic, the “anti vaccine” crowd are claiming that we could reduce autism if only we could get our debt under control – or are they claiming vice versa – that autism is causing the Federal Debt ?

    Examining dairy consumption (*1) shows a :
    – 0.82 Autism Correlation with Milk Consumption
    +0.92 Autism Correlation with Yogurt Consumption
    So apparently (by anti vaccine logic) to reduce autism we need to drink more milk, but eat less yogurt.

    Of course that also means that the Federal Debt has a -0.91 correlation with milk consumption, and a +0.98 correlation with yogurt consumption, so by drinking more milk but eating less yogurt, not only do we cure autism but abolish the Federal Debt.

    (*1) Dairy Consumption http://www.ers.usda.gov/data-products/dairy-data.aspx

  2. We forget that correlation is also not “not causation.”

    Do we really think people are so dumb? They take aspirin and Advil, but you never hear people say “aspirin caused these adverse events.” People take all kinds of prescription drugs, and side effects are acknowledged, and yet people don’t go around blaming these drugs for serious harms. Only in the world of vaccines are side effects dismissed and parents told they are imagining things, because “correlation isn’t causation.” Well, I hate to say it but it’s also not “non-causation,” so to use this as a way to dismiss real harms disingenuous.

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