Archive for the pictures Category

snapshot from Salem

Posted in Kids, pictures, Travel with tags , , , , , , , on October 31, 2014 by xi'an

Salem

reliable ABC model choice via random forests

Posted in pictures, R, Statistics, University life with tags , , , , , , , on October 29, 2014 by xi'an

human_ldaAfter a somewhat prolonged labour (!), we have at last completed our paper on ABC model choice with random forests and submitted it to PNAS for possible publication. While the paper is entirely methodological, the primary domain of application of ABC model choice methods remains population genetics and the diffusion of this new methodology to the users is thus more likely via a media like PNAS than via a machine learning or statistics journal.

When compared with our recent update of the arXived paper, there is not much different in contents, as it is mostly an issue of fitting the PNAS publication canons. (Which makes the paper less readable in the posted version [in my opinion!] as it needs to fit the main document within the compulsory six pages, relegated part of the experiments and of the explanations to the Supplementary Information section.)

projective covariate selection

Posted in Mountains, pictures, Statistics, Travel, University life with tags , , , , , , , , , , , , , , on October 28, 2014 by xi'an

While I was in Warwick, Dan Simpson [newly arrived from Norway on a postdoc position] mentioned to me he had attended a talk by Aki Vehtari in Norway where my early work with Jérôme Dupuis on projective priors was used. He gave me the link to this paper by Peltola, Havulinna, Salomaa and Vehtari that indeed refers to the idea that a prior on a given Euclidean space defines priors by projections on all subspaces, despite the zero measure of all those subspaces. (This notion first appeared in a joint paper with my friend Costas Goutis, who alas died in a diving accident a few months later.) The projection further allowed for a simple expression of the Kullback-Leibler deviance between the corresponding models and for a Pythagorean theorem on the additivity of the deviances between embedded models. The weakest spot of this approach of ours was, in my opinion and unsurprisingly, about deciding when a submodel was too far from the full model. The lack of explanatory power introduced therein had no absolute scale and later discussions led me to think that the bound should depend on the sample size to ensure consistency. (The recent paper by Nott and Leng that was expanding on this projection has now appeared in CSDA.)

“Specifically, the models with subsets of covariates are found by maximizing the similarity of their predictions to this reference as proposed by Dupuis and Robert [12]. Notably, this approach does not require specifying priors for the submodels and one can instead focus on building a good reference model. Dupuis and Robert (2003) suggest choosing the size of the covariate subset based on an acceptable loss of explanatory power compared to the reference model. We examine using cross-validation based estimates of predictive performance as an alternative.” T. Peltola et al.

The paper also connects with the Bayesian Lasso literature, concluding on the horseshoe prior being more informative than the Laplace prior. It applies the selection approach to identify biomarkers with predictive performances in a study of diabetic patients. The authors rank model according to their (log) predictive density at the observed data, using cross-validation to avoid exploiting the data twice. On the MCMC front, the paper implements the NUTS version of HMC with STAN.

more geese…

Posted in pictures, Running with tags , on October 19, 2014 by xi'an

art brut

Posted in Kids, pictures, Travel with tags , , , , on October 18, 2014 by xi'an

barbacycle

6th French Econometrics Conference in Dauphine

Posted in Books, Kids, pictures, Statistics, University life with tags , , , , , , , on October 15, 2014 by xi'an

La Défense, from Paris-Dauphine, May 2009

On December 4-5, Université Paris-Dauphine will host the 6th French Econometric Conference, which celebrates Christian Gouriéroux and his contributions to econometrics. (Christian was my statistics professor during my graduate years at ENSAE and then Head of CREST when I joined this research unit, first as a PhD student and later as Head of the statistics group. And he has always been a tremendous support for me.)

Not only is the program quite impressive, with co-authors of Christian Gouriéroux and a few Nobel laureates (if not the latest, Jean Tirole, who taught economics at ENSAE when I was a student there), but registration is free. I will most definitely attend the talks, as I am in Paris-Dauphine at this time of year (the week before NIPS). In particular, looking forward to Gallant’s views on Bayesian statistics.

my ISBA tee-shirt designs

Posted in Books, Kids, pictures, Statistics, University life with tags , , , , , , , on October 15, 2014 by xi'an

Here are my tee-shirt design proposals for the official ISBA tee-shirt competition! (I used the facilities of CustomInk.com as I could not easily find a free software around. Except for the last one where I recycled my vistaprint mug design…)

meetherevtmeetherevbklifeisjokebklifeisjokesignaturesignaturebkwerewolves

While I do not have any expectation of seeing one of these the winner (!), what is your favourite one?!

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