Archive for long distance running

running shoes

Posted in Books, Running, Statistics with tags , , , , , , , , , , on August 12, 2018 by xi'an

A few days ago, when back from my morning run, I spotted a NYT article on Nike shoes that are supposed to bring on average a 4% gain in speed. Meaning for instance a 3 to 4 minute gain in a half-marathon.

“Using public race reports and shoe records from Strava, a fitness app that calls itself the social network for athletes, The Times found that runners in Vaporflys ran 3 to 4 percent faster than similar runners wearing other shoes, and more than 1 percent faster than the next-fastest racing shoe.”

What is interesting in this NYT article is that the two journalists who wrote it have analysed their own data, taken from Strava. Using a statistical model or models (linear regression? non-linear regression? neural net?) to predict the impact of the shoe make, against “all” other factors contributing to the overall time or position or percentage gain or yet something else. In most analyses produced in the NYT article, the 4% gain is reproduced (with a 2% gain for female shoe switcher and a 7% gain for slow runners).

“Of course, these observations do not constitute a randomized control trial. Runners choose to wear Vaporflys; they are not randomly assigned them. One statistical approach that seeks to address this uses something called propensity scores, which attempt to control for the likelihood that someone wears the shoes in the first place. We tried this, too. Our estimates didn’t change.”

The statistical analysis (or analyses) seems rather thorough, from what is reported in the NYT article, with several attempts at controlling for confounders. Still, the data itself is observational, even if providing a lot of variables to run the analyses, as it only covers runners using Strava (from 5% in Tokyo to 25% in London!) and indicating the type of shoes they wear during the race. There is also the issue that the shoes are quite expensive, at $250 a pair, especially if the effect wears out after 100 miles (this was not tested in the study), as I would hesitate to use them unless the race conditions look optimal (and they never do!). There is certainly a new shoes effect on top of that, between the real impact of a better response and a placebo effect. As shown by a similar effect of many other shoe makes. Hence, a moderating impact on the NYT conclusion that these Nike Vaporflys (flies?!) are an “outlier”. But nonetheless a fairly elaborate and careful statistical study that could potentially make it to a top journal like Annals of Applied Statistics!

bad graph of Olympic proportions

Posted in Books, Kids, pictures, Running with tags , , , , on August 14, 2016 by xi'an

olympicsIn connection with the current Olympics in Rio, the New York Times produced a sequence of graphs displaying the dominance of some countries for some sports, like the above for long distance running. I find the representation pretty poor, from using a continuous time perspective for 30 Olympic events, to an unexplained colour codes singling out a few countries, to an equally unexplained second axis, with an upward drift above that does not seem to make sense…

should I run less?!

Posted in Running, Statistics with tags , , , on February 10, 2015 by xi'an

Run_ABCA study [re]published three days ago in both The New York Times and the BBC The Guardian reproduced the conclusion of an article in the Journal of the American College of Cardiology that strenuous and long-distance jogging (or more appropriately running) could have a negative impact on longevity! And that the best pace is around 8km/h, just above a brisk walk! Quite depressing… However, this was quickly followed by other articles, including this one in The New York Times, pointing out the lack of statistical validation in the study and the ridiculously small number of runners in the study. I am already feeling  better (and ready for my long run tomorrow morning!), but appalled all the same by the lack of standards of journals publishing statistically void studies. I know, nothing new there…