Back in May 2002, the BBC ran a story affirming that breast-milk boosts babies’ brainpower. The central claim of the article was this: “The longer a baby is breast-fed the more intelligent it is likely to be.”

This claim was supported by a statistical analysis. Danish and American researchers had recorded how individuals were fed as babies, measured their IQs as adults, and found a connection.

Statistically, babies that were breast-fed for less than a month had below-average IQs. IQ increased proportionally to how long babies were breast-fed up to nine months, after which it tapered off.

On this basis, the conclusion was drawn: breast-feeding for the first nine-months of a baby’s life increases its intelligence.

Four years later, the flaw in this reasoning has been spotted, and a new story has been run. This time the headline is “Breast Milk does not Boost IQ”.

The more recent article explains that the breast-fed babies are not more intelligent because they are breast-fed, but because breast-feeding mothers tend to be more intelligent, educated, and affluent. These qualities are passed on to the children through genetic and other means, but there is no evidence to indicate that they are passed on by breast-feeding.

In other words, the original study committed the correlation not causation fallacy, mistaking a statistical correlation for a causal link.