arnab gupta

Confusing correlation with causation

June 18, 2012

One of my pet peeves with scientific journalism is the propensity to confuse correlation with causation. The idea is that just because two things are observed to happen at the same time (or before, or after, one another), does not imply that one causes the other.

In the latest example of this, the link between chocolate and good health is revisited.

The article opens with:

People who eat chocolate regularly tend to be thinner, new research suggests.

… which implies that a causation has been observed. The article goes on to make the following points:

[…] those who ate chocolate a few times a week were, on average, slimmer than those who ate it occasionally.

The link remained even when other factors, like how much exercise individuals did, were taken into account.

[…] it is how often you eat chocolate that is important, rather than how much of it you eat. The study found no link with quantity consumed.

So… I’d still lose weight if I ate a tonne of chocolate very frequently? Really?!

The most important statement, however, comes a little later:

But the findings only suggest a link - not proof that one factor causes the other.

… and,

And if you are looking to change your diet, you are likely to benefit most from eating more fresh fruits and vegetables.

Now guess what the headline of this article, which itself says that it’s only a link, and talks about maintaining an overall good diet, reads.

Chocolate ‘may help keep people slim’

Perfect, isn’t it?