Does playing tennis make you live 9.7 years longer?
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What is the main topic discussed in this episode?
Hello, and thanks for downloading the More or Less podcast. We're the programme that helps you take a swing at suspicious numbers, challenge data that seems clearly out, and return statistical sanity. I'm your umpire, Tim Harford. Recently, a post did the rounds on Twitter that claimed that if you do this… you might live 9.7 years longer. First things first, the claim does come from a peer-reviewed paper by a group of doctors and scientists from the Mayo Clinic. The team used data from Denmark to follow a group of people and try and work out which sport produced the most gains in years lived. They looked at eight different sports and found that people could expect to gain...
9.7 years of life from playing tennis, 6.2 for badminton, 4.7 for soccer, 3.7 for cycling, 3.4 for swimming, 3.2 for jogging, 3.1 for calisthenics and 1.5 for health club activities.
That last one sounds ominous. So tennis could extend your life five years more than jogging could. Or could it? People on the internet were quick to point out that doing this is in many countries an expensive and elitist sport. Now, it is a well-established fact that people who are wealthier and have a higher level of education tend to live longer. So the commenters argued, are our balls in the wrong court? Is longevity just an artefact of socioeconomic status?
What claim about tennis and longevity went viral on Twitter?
Or is tennis truly responsible for longer lives? To answer this, we need to look into the data. So, in the spirit of Wimbledon, we've done just that.
So I'm Adam Jacobs. I'm a medical statistician. I've been working in clinical trials for about 30 years.
As far as these types of studies go, Adam says the one this claim came from is quite a good one. So there are several good things about this study.
See? It's a large study. They had over 8,000 participants in it, and they had a long follow-up time, which is really good.
Where did the 9.7 years figure come from and what data did researchers use?
They followed people for 25 years, which means that a lot of people are going to die in that time. So you get good data on all-cause mortality, which was their primary outcome measure. And that's a good primary outcome measure because it's unambiguous and everybody knows it's relevant.
But what of the twits earlier point that tennis is often played by people with university degrees and exceptional health care who, by the way, tend to live longer? How do we make sure that someone's socioeconomic status isn't clouding things?
Yeah, so that's called confounding. So that may explain some of the association. And it probably does. I don't think it's as big a deal as I first thought it was when I saw the paper. They do an unadjusted analysis where they do not adjust for socioeconomic status.
They do this through witchcraft and wizardry, aka hazard regression models.
Well, that's statistical magic, basically. What we do is we analyse it in a statistical model. You can do a statistical model, and this one, the thing is called Cox Proportional Hazards Regression, and that's a very widely used statistical model for... analyzing survival data, and that allows you to just plug these confounding variables into the model. And what it tells you is what would the effect be if all the confounding variables were the same between the people who play tennis and people who don't play tennis.
How did the study rank life‑expectancy gains across different sports?
And in that analysis, they found that the people who played tennis got 10.4 more years of life expectancy than the people who didn't play tennis. They then adjusted that for education and income and a couple of other things. And that went down to 9.7.
Now, the model wasn't perfect. They lost almost a third of people from the tennis group. We don't really know why this happened, but it's likely to do with insufficient data. Still, if you look at the group before and after the attempted flattening of people's education levels, wealth and so on, the numbers are surprisingly similar. The group of tennis players without adjustments lived an extra 10.4 years, as opposed to 9.7. Not a huge difference.
That tells me maybe it's not a massively strong confounding here, which surprised me.
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Chapters
4 chapters
1
What is the main topic discussed in this episode?
0:00–1:43
2
What claim about tennis and longevity went viral on Twitter?
1:43–2:20
3
Where did the 9.7 years figure come from and what data did researchers use?
2:20–3:48
4
How did the study rank life‑expectancy gains across different sports?
3:48–8:53