Archive for Fushimi Inari-Taihsa shrine

Kant, Platon, Bayes, & Le Monde…

Posted in Books, Statistics, University life with tags , , , , , , , , , , , , on July 2, 2012 by xi'an

In the weekend edition of Le Monde I bought when getting out of my plane back from Osaka, and ISBA 2012!, the science leaflet has a (weekly) tribune by a physicist called Marco Zito that discussed this time of the differences between frequentist and Bayesian confidence intervals. While it is nice to see this opposition debated in a general audience daily like Le Monde, I am not sure the tribune will bring enough light to help to the newcomer to reach an opinion about the difference! (The previous tribune considering Bayesian statistics was certainly more to my taste!)

Since I cannot find a link to the paper, let me sum up: the core of the tribune is to wonder what does 90% in 90% confidence interval mean? The Bayesian version sounds ridiculous since “there is a single true value of [the parameter] M and it is either in the interval or not” [my translation]. The physicist then goes into stating that the probability is in fact “subjective. It measures the degree of conviction of the scientists, given the data, for M to be in the interval. If those scientists were aware of another measure, they would use another interval” [my translation]. Darn… so many misrepresentations in so few words! First, as a Bayesian, I most often consider there is a true value for the parameter associated with a dataset but I still use a prior and a posterior that are not point masses, without being incoherent, simply because the posterior only summarizes what I know about the  parameter, but is obviously not a property of the true parameter. Second, the fact that the interval changes with the measure has nothing to do with being Bayesians. A frequentist would also change her/his interval with other measures…Third, the Bayesian “confidence” interval is but a tiny (and reductive) part of the inference one can draw from the posterior distribution.

From this delicate start, things do not improve in the tribune: the frequentist approach is objective and not contested by Marco Zito, as it sounds eminently logical. Kant is associated with Bayes and Platon with the frequentist approach, “religious wars” are mentioned about both perspectives debating endlessly about the validity of their interpretation (is this truly the case? In the few cosmology papers I modestly contributed to, referees’ reports never objected to the Bayesian approach…) The conclusion makes one wonders what is the overall point of this tribune: superficial philosophy (“the debate keeps going on and this makes sense since it deals with the very nature of research: can we know and speak of the world per se or is it forever hidden to us? (…) This is why doubt and even distrust apply about every scientific result and also in other settings.”) or criticism of statistics (“science (or art) of interpreting results from an experiment”)? (And to preamp a foreseeable question: no, I am not writing to the journal this time!)

ISBA 2012 [#2]

Posted in pictures, Statistics, Travel, University life with tags , , , , , , , on June 28, 2012 by xi'an

As I slept more than three hours last night, I managed to stay concentrated for a larger portion of the talks today, if missing my morning run! Sam Clifford already discussed some of the sessions I attended, with the same impression about Tamara Broderick’s talk: this was an exceptional and brilliant talk, where the focus was absolutely right and avoided technicalities while conveying the ideas (my candidate for the Lindley prize for sure!). I also like Niels Hjort’s survey and reminiscence, delivered in his unique style! The second session about big data was also quite interesting as it addressed a true problem I feel concerned about if unable to provide useful advances… Michael Jordan’s idea of bags of little bootstraps was neat and concretised the vague notions I had of splitting the data into little datasets. It also opened new directions for thinking, quite appropriately since Michael will spend next year in Paris!

Wanting very much to see the Fushimi Inari-Taisha shrine and its red pilars, I shamefully skipped Chris Holmes’ plenary lecture (and hope Chris will pardon me, one day..!). The shrine was actually quite spectacular while a walking distance from the conference (due East, about 20mn). I even managed to take “empty” pictures despite the crowd. The two afternoon sessions on random probabilities and “honest” MCMC were also quite to my taste, again opening news vistas and raising questions. I also managed to take a peek at most posters, even though another hour would have been welcomed, and got several great exchanges along the way.

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