Thinking Twice About Causality

Two completely unrelated headlines provide a reminder to think twice about causality. The Washington Post proclaimed “The More Sex You Have, the More Money You Make.” And then Nikhil Dhurandhar, Vice-President of the Obesity Society, sparked a story on Good Morning America about 84 different potential causes of obesity.

Wishful thinking has a lot to do with jumping to assume that an association means that we’ve found a cause. And no doubt, the study that found a strong association between frequency of sex and income fostered some wishful thinking. But that’s all it is — wishful thinking and a strong association.

Likewise, for many of the putative causes of obesity, all we have is an association and lots of people who are sure there must be a cause and effect relationship at work.

One of the oft-repeated associations with obesity is breast feeding. Multiple studies show an association between breast feeding and a reduced risk of obesity. But controlled studies to test cause and effect are pretty consistent in finding no effect. Breast feeding offers many well-documented benefits, so people who know better tend to add obesity prevention to the list. But selling an idea based on shaky claims seldom works out well.

Another association with obesity in the headlines this week is the association between two compounds from food packaging — BPA and DEHP — and insulin resistance or obesity. Martin Binks wisely reminds us that the association might have something to do with the caloric content of the packaged foods that presumably carry these compounds.

What we need is a stronger commitment to research that actually proves cause and effect in obesity. We have plenty of associations.

Click here to read more in the Washington Post, click here to read more from Good Morning America, click here to read more from MedPage Today, and click here to read the study of sex and income.

Popcorn Mike, photograph © Viewminder / flickr

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