Archive for Porte Dauphine

simplified Bayesian analysis

Posted in Statistics with tags , , , , , , , , , , , , on February 10, 2021 by xi'an

A colleague from Dauphine sent me a paper by Carlo Graziani on a Bayesian analysis of vaccine efficiency, asking for my opinion. The Bayesian side is quite simple: given two Poisson observations, N~P(μ) and M~P(ν), there exists a reparameterisation of (μ,ν) into

e=1-μ/rν  and  λ=ν(1+(1-e)r)=μ+ν

vaccine efficiency and expectation of N+M, respectively, when r is the vaccine-to-placebo ratio of person-times at risk, ie the ratio of the numbers of participants in each group. Reparameterisation such that the likelihood factorises into a function of e and a function of λ. Using a product prior for this parameterisation leads to a posterior on e times a posterior on λ. This is a nice remark, which may have been made earlier (as for instance another approach to infer about e while treating λ as a nuisance parameter is to condition on N+M). The paper then proposes as an application of this remark an analysis of the results of three SARS-Cov-2 vaccines, meaning using the pairs (N,M) for each vaccine and deriving credible intervals, which sounds more like an exercise in basic Bayesian inference than a fundamental step in assessing the efficiency of the vaccines…

to bike or not to bike

Posted in Kids, pictures, Running, Travel with tags , , , , , , , , , on March 22, 2020 by xi'an

A recent debate between the candidates to the Paris mayorship, including a former Health minister and physician, led to arguments as to whether or not biking in Paris is healthy. Obviously, it is beneficial for the community, but the question is rather about the personal benefits vs dangers of riding a bike daily to work. Extra physical activity on the one hand, exposition to air pollution and accidents on the other hand. With an accident rate that increased during the recent strikes, but at a lesser rate (153%) than the number of cyclists in the streets of Paris (260%). While I do not find the air particularly stinky or unpleasant on my daily 25km, except in the frequent jams between Porte d’Auteuil and Porte de la Muette, and while I haven’t noticed a direct impact on my breathing or general shape, I try to avoid rush hours, especially on the way back home with a good climb near Porte de Versailles (the more on days when it is jammed solid with delivery trucks for the nearby exhibition centre). As for accidents, trying to maintain constant vigilance and predicting potential fishtails is the rule, as is avoiding most bike paths as I find them much more accident-prone than main streets… (Green lights are also more dangerous than red lights, in my opinion!) Presumably, so far at least, benefits outweight the costs!

…place Dauphine…il est cinq heures, Paris s’éveille [jatp]

Posted in pictures, Travel, Wines with tags , , , , , , , , , , on November 21, 2019 by xi'an

free Fall

Posted in Statistics with tags , , , , , , , on September 15, 2018 by xi'an

Summer is off, Fall is back, as now the open air swimming pool has closed, the park opens too late for my schedule, shorts have all but disappeared from the streets and classrooms, the last raspberries have dried out, green tomatoes in my garden are unlikely to get any redder, the ant traps are no longer needed, the watering hose has been stored inside along the umbrella, and eating outdoors becomes a challenge, but the return from the traditional August vacation break has seen an explosion in the number of cyclists on my way to Dauphine, meaning I end up on most trips biking with (or against) other [100% nuke free] cyclists, with an improved trip duration (if not safer trips!). And no connection with the free fall tee!

computer strategies for complex Bayesian models

Posted in Books, Kids, Statistics, University life with tags , , , , , , , , on July 18, 2016 by xi'an

frontThis is the cover page of Marco Banterle‘s thesis, who will defend on Thursday [July 21, 13:00], at a rather quiet time for French universities, which is one reason for advertising it here. The thesis is built around several of Marco’s papers, like delayed acceptance, dimension expansion, and Gaussian copula for graphical models. The defence is open to everyone, so feel free to join if near Paris-Dauphine!