Archive for USA

US elections [xkcd repost]

Posted in Books, Kids, Travel with tags , , , , , , on November 6, 2018 by xi'an

Randall Munroe of xkcd has designed this massive map of the US elections with links to all candidates and random places that I first mistook for voting stations (this would have been great!, to highlight how would-be voters can be discouraged from voting in some districts), as well as a few hidden comics and places irrelevant for the elections. (Warning: The above is a static copy!) With the great subtext that to edit the map readers need to submit their ballot before on November 7th.

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!

precisely!

Posted in pictures, Travel with tags , , , , , , on January 12, 2018 by xi'an

U of T sunset [jatp]

Posted in pictures, Running, Travel, University life with tags , , , , , on December 14, 2017 by xi'an

O’Bayes 2017 group photograph

Posted in pictures, Statistics, Travel, University life with tags , , , , , , , , on December 13, 2017 by xi'an

off to Austin!

Posted in Books, Kids, Statistics, Travel, University life, Wines with tags , , , , , , , , , on December 9, 2017 by xi'an

Today I am flying to Austin, Texas, on the occasion of the O’Bayes 2017 conference, the 12th meeting in the series. In complete objectivity (I am a member of the scientific committee!), the scientific program looks quite exciting, with new themes and new faces. (And Peter Müller concocted a special social program as well!) As indicated above [with an innovative spelling of my first name!] I will give my “traditional” tutorial on O’Bayes testing and model choice tomorrow, flying back to Paris on Wednesday (and alas missing the final talks, including Better together by Pierre!). A nice pun is that the conference centre is located on Robert De[a]dman Drive, which I hope is not premonitory of a fatal ending to my talk there..!

Monty Hall closes the door

Posted in Books, Kids, pictures with tags , , , , , , , , , on October 1, 2017 by xi'an

Among much more dramatic news today, I learned about Monty Hall passing away, who achieved long lasting fame among probabilists for his TV game show leading to the Monty Hall problem, a simple conditional probability derivation often leading to arguments because of the loose wording of the conditioning event. By virtue of Stigler’s Law, the Monty Hall game was actually invented earlier, apparently by the French probabilist Joseph Bertrand, in his Calcul des probabilités. The New York Times article linked with the image points out the role of outfits with the game participants, towards being selected by the host, Monty Hall. And that one show had a live elephant behind a door, instead of a goat, elephant which freaked out..!