Archive for bicycle

don’t wear your helmet, you could have a bike accident!

Posted in Kids, Running, Statistics, Travel with tags , , , , , , , , , , , on January 18, 2022 by xi'an

As once in a while reappears the argument that wearing a bike helmet increases one’s chances of a bike accident. In the current case, it is to argue against a French regulation proposal that helmets should be compulsory for all cyclists. Without getting now into the pros and cons of compulsory helmet laws (enforced in Argentina, Australia, and New Zealand, as well as some provinces of Canada), I see little worth in the study cited by Le Monde towards this argument. As the data is poor and poorly analysed. First, there is a significant fraction of cycling accidents when the presence of an helmet is unknown. Second, the fraction of cyclists wearing helmets is based on a yearly survey involving 500 persons in a few major French cities. The conclusion that there are three times more accidents among cyclists wearing helmets than among cyclists not wearing helmets is thus not particularly reliable. Rather than the highly debatable arguments that (a) seeing a cyclist with an helmet would reduce the caution of car or bus drivers, (b) wearing an helmet would reduce the risk aversion of a cyclist, (c) sport-cyclists are mostly wearing helmets but their bikes are not appropriate for cities (!), I would not eliminate [as the authors do] the basic argument that helmeted cyclists are on average traveling longer distances. With a probability of an accident that necessarily  increases with the distance traveled. While people renting on-the-go bikes are usually biking short distances and almost never wear helmets. (For the record, I mostly wear a [bright orange] helmet but sometimes do not when going to the nearby bakery or swimming pool… Each time I had a fall, crash or accident with a car, I was wearing an helmet and I once hit my head or rather the helmet on the ground, with no consequence I am aware of!)

What is luck? [book review]

Posted in Books, Statistics, Travel, University life with tags , , , , , , , , , , , , , , , , , , , , , , , , on December 10, 2021 by xi'an

I was sent—by Columbia University Press—this book for a potential review in CHANCE: What are the chances? (Why we believe in luck?) was written by Barbara Blatchley, professor of Psychology and Neuroscience at Agnes Scott College in Decatur, Georgia. I have read rather quickly its 193 pages over the recent trips I made to Marseille and Warwick. The topic is truly about luck and the psychology of the feeling of being luck or unlucky. There is thus rather little to relate to as a statistician, as this is not a book about chance! (I always need to pay attention when using both words, since, in French chance primarily means luck, while malchance means bad luck. And the French term for chance and randomness is hasard…) The book is pleasant to read, even though the accumulation of reports about psychological studies may prove tiresome in the long run and, for a statistician, worrisome as to which percentage of such studies were properly validated by statistical arguments…

“…the famous quote by Louis Pasteur: “Dans les champs de l’observation, le hasard ne favorise que les esprits préparés”s (…) Pasteur never saw a challenge he couldn’t overcome with patience and preparation.” (p.19)

Even the part about randomness is a-statistical and mostly a-probabilist, rather focusing on our subjective and biased (un)ability to judge randomness. The author introduces us to the concepts of apophenia, which is “the unmotivated seeing of connections accompanied with a specific feeling of abnormal meaningfulness”, and of patternicity for the “tendency to find meaningful patterns in meaningless noise”. She also states that (Neyman-Pearson) Type I error is about seeing a pattern in random noise while Type II errors are for conclusion of meaningless when the data is meaningful (p.15). Which is reductive to say the least, but lead her to recall the four types of luck proposed by James Austin (which I first misread as Jane Austin).

“There is a long-standing and deeply intimate connection between luck, religion, and belief in the supernatural.” (p.28)

I enjoyed very much the sections on these connections between a belief in luck and religions, even though the anthropological references to ancient religions are not strongly connected to luck, but rather to the belief that gods and goddesses could modify one’s fate (and avoiding the most established religions). Still, I appreciate her stressing the fact that if one believes in luck (as opposed to sheer randomness), this expresses at the very least a form of irrational belief in higher powers that can bend randomness in one’s favour (or disfavour). Which is the seed for more elaborate if irrational beliefs. (For illustrations, Borgès’ stories come to mind.)

“B.F. Skinner believed that superstitious behaviour was a consequence of learning and reinforcement.” (p.85)

There are also parts where (a belief in) luck and (human) learning are connected, but, unfortunately, no mention is made of the (vaguely) Bayesian nature of the (plastic, p. 188) brain modus operandi. The large section on the brain found in the book is instead physiological, since concerned with finding regions where the belief in luck could be located. In relation with attention-deficit disorders. (Revealing the interesting existence (for me) of mirror neurons, dedicated to predicting what could happen! Described as “predictive coding”, p.153). The last chapter “How to get lucky” contains a rather lengthy account of “Clever Hans”, the 1990 German counting horse (!). Who, as well-known, reacted to subtle and possibly unconscious signals from his trainer rather than to an equine feeling for arithmetic…

One of the clearest conclusions of the book is (imho) that a belief in luck may improve the life of the believers, while a belief in being unlucky may deteriorate it. The Taoist tale finishing the book is a pure gem. But I am still in the dark as to whether or not my exceptional number of bike punctures in the past year qualifies as bad luck!

“Luck is the way you face the randomness of the world.” (p.191)

As an irrelevant aside, one anecdote at the beginning of the book brought back memories of the Wabash River flowing through Lafayette, IN, as it tells of the luck of two Purdue female rowers who attempted a transatlantic race and survived capsizing in the middle of the Atlantic. It also made me regret I had not realised at the time there was a rowing opportunity there!

`Paris is in anarchy’ [cycle woes]

Posted in Travel with tags , , , , , , , , , , on October 7, 2021 by xi'an

An overblown view of the cycling war in Paris, from New York! I read with amusement the report on how Xing a Parisian street is a matter of life or death, when anarclists go through red lights while shouting at pedestrians… Actually, the figures show that the number of accidents involving cyclists (as victims or culprits) has only gone up by 30% when the traffic has increased by 70%. And I could not find an online trace of a pedestrian killed by a cyclist over the past years. Based on my weekly 130 kilometer biking average, mostly to and from Paris Dauphine, I do not perceive a major tension between pedestrians and cyclists, maybe because I am not entering the centre of town (and give priority to pedestrians at both green and red lights). The danger in my experience comes rather from other cyclists’ unpredictable paths, (psychopath) mopeds that run on cycle paths, and cars turning right without checking for bicycles. But I concur with the point made in this article of a poor network of cycle paths, with too many discontinuities, bad surface, inexistent maintenance (esp. in winter months when wet leaves accumulate there and all year long for broken glass and metal parts), and the deadly pavés! Which are unpleasant for road bikes (ask the Paris-Roubaix runners!), slippery, esp. when frosted (speaking from experience), and damaging to tubes and ties. As it happens, I have had thee tube punctures over the three past weeks, two of which were due to running over a particularly uneven pavé or entering a cycle path with a very high step. (And a total of six since April. Making me reconsider using an heavier mountain bike instead. After switching unsuccessfully to anti-puncture road tyres…)

30 less reasons to overtake bikes

Posted in pictures, Running, Travel with tags , , , , , , , on September 17, 2021 by xi'an

Wagram, morne plaine!

Posted in Books, Kids, pictures, Running with tags , , , , , , , , on November 20, 2020 by xi'an

Avenue de Wagram is one of the avenues leaving from Arc de Triomphe in Paris, named after a (bloody) Napoléonic battle (1809). This is also where I locked my bike today before joining my son for a quick lunch and where I found my back wheel completely dismantled when I came back!  Not only the wheel had been removed from the frame, but the axle had been taken away, damaging the ball bearing… After much cursing, I looked around for the different pieces and remounted the wheel on the bike. The return home to the local repair shop was slower than usual as the wheel was acting as a constant brake. I am somewhat bemused at this happening in the middle of the day, on a rather busy street and at the motivation for it. Disgruntled third year student furious with the mid-term exam? Unhappy author after a Biometrika rejection?

Not a great week for biking since I also crashed last weekend on my way back from the farmers’ market when my pannier full of vegetables got caught in between the spokes. Nothing broken, apart from a few scratches and my cell phone screen… [Note: the title is stolen from Hugo’s Waterloo! Morne plaine!, a terrible and endless poem about the ultimate battle of Napoléon in 1815. With a tenth of the deaths at Wagram… Unsurprisingly, no Avenue de Waterloo leaves from Arc de Triomphe! ]

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