Does racquetball save lives?

October 12, 2017
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(This article was originally published at Statistical Modeling, Causal Inference, and Social Science, and syndicated at StatsBlogs.)

Asher Meir points to this news report and writes:

8e5 people in study, about half reported exercising, about half not. About 10% died overall. So overall death rate difference of 28% is pretty remarkable. It means about 3500 deaths instead of 4500 for a similar sample size.

But when you compare the rate of heart disease risk specifically (about 2% died of heart disease, or around 1000 in each sample), for runners vs. racket sports specifically (less than 10% each) you are really shooting in the dark. Say around 5000 people engaged in each kind of activity and around 100 died of heart disease in each group, sounds like normal variation.

Also they eliminated people who had heart disease at the beginning of the study, not sure why they would do this.

I guess the biggest issue is not controlling for endogeneity of activity, as the people who are frail and sickly are probably not engaging in much sports activity.

Not sure how much is author hype vs. journalist hype.

My reply: This reminds me of the “what does not kill me makes me stronger” principle. The elimination of people with risk at beginning of study, that’s interesting. I can see why it makes sense to do this and I can also see how it can cause bias. I guess the right way to do this is to express results conditional on initial risk.

Meir:

Afterwards I realized the biggest weakness: They do not control for income. If you examine the results you see that the people who engage in the most expensive forms of exercise (e.g. racquetball) have the lowest morbidity. Could be just a proxy for income.

Anyway, a flawed study is better than no study, the next time they can try to control for income.

Yup. Gotta start somewhere. Make all your data and code available, don’t hype your claims, and we can go from there.

P.S. Meir also pointed me to this book, “The Lion in the Living Room: How House Cats Tamed Us and Took Over the World,” by Abigail Tucker. I haven’t read it—really I should spend less time online and more time reading books!—but it has a pretty good title, I’ll grant it that.

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