Archive for Journal of the Royal Statistical Society

visual effects

Posted in Books, pictures, Statistics with tags , , , , , , , , , , , on November 2, 2018 by xi'an

As advertised and re-discussed by Dan Simpson on the Statistical Modeling, &tc. blog he shares with Andrew and a few others, the paper Visualization in Bayesian workflow he wrote with Jonah Gabry, Aki Vehtari, Michael Betancourt and Andrew Gelman was one of three discussed at the RSS conference in Cardiff, last week month, as a Read Paper for Series A. I had stored the paper when it came out towards reading and discussing it, but as often this good intention led to no concrete ending. [Except concrete as in concrete shoes…] Hence a few notes rather than a discussion in Series B A.

Exploratory data analysis goes beyond just plotting the data, which should sound reasonable to all modeling readers.

Fake data [not fake news!] can be almost [more!] as valuable as real data for building your model, oh yes!, this is the message I am always trying to convey to my first year students, when arguing about the connection between models and simulation, as well as a defense of ABC methods. And more globally of the very idea of statistical modelling. While indeed “Bayesian models with proper priors are generative models”, I am not particularly fan of using the prior predictive [or the evidence] to assess the prior as it may end up in a classification of more or less all but terrible priors, meaning that all give very little weight to neighbourhoods of high likelihood values. Still, in a discussion of a TAS paper by Seaman et al. on the role of prior, Kaniav Kamary and I produced prior assessments that were similar to the comparison illustrated in Figure 4. (And this makes me wondering which point we missed in this discussion, according to Dan.)  Unhappy am I with the weakly informative prior illustration (and concept) as the amount of fudging and calibrating to move from the immensely vague choice of N(0,100) to the fairly tight choice of N(0,1) or N(1,1) is not provided. The paper reads like these priors were the obvious and first choice of the authors. I completely agree with the warning that “the utility of the the prior predictive distribution to evaluate the model does not extend to utility in selecting between models”.

MCMC diagnostics, beyond trace plots, yes again, but this recommendation sounds a wee bit outdated. (As our 1998 reviewww!) Figure 5(b) links different parameters of the model with lines, which does not clearly relate to a better understanding of convergence. Figure 5(a) does not tell much either since the green (divergent) dots stand within the black dots, at least in the projected 2D plot (and how can one reach beyond 2D?) Feels like I need to rtfm..!

“Posterior predictive checks are vital for model evaluation”, to wit that I find Figure 6 much more to my liking and closer to my practice. There could have been a reference to Ratmann et al. for ABC where graphical measures of discrepancy were used in conjunction with ABC output as direct tools for model assessment and comparison. Essentially predicting a zero error with the ABC posterior predictive. And of course “posterior predictive checking makes use of the data twice, once for the fitting and once for the checking.” Which means one should either resort to loo solutions (as mentioned in the paper) or call for calibration of the double-use by re-simulating pseudo-datasets from the posterior predictive. I find the suggestion that “it is a good idea to choose statistics that are orthogonal to the model parameters” somewhat antiquated, in that this sounds like rephrasing the primeval call to ancillary statistics for model assessment (Kiefer, 1975), while pretty hard to implement in modern complex models.

free and graphic session at RSS 2018 in Cardiff

Posted in pictures, Statistics, Travel, University life with tags , , , , , , , on July 11, 2018 by xi'an

Reposting an email I received from the Royal Statistical Society, this is to announce a discussion session on three papers on Data visualization in Cardiff City Hall next September 5, as a free part of the RSS annual conference. (But the conference team must be told in advance.)

Paper:             ‘Visualizing spatiotemporal models with virtual reality: from fully immersive environments to applications in stereoscopic view

Authors:         Stefano Castruccio (University of Notre Dame, USA) and Marc G. Genton and Ying Sun (King Abdullah University of Science and Technology, Thuwal)

 Paper:             Visualization in Bayesian workflow’

Authors:            Jonah Gabry (Columbia University, New York), Daniel Simpson (University of Toronto), Aki Vehtari (Aalto University, Espoo), Michael Betancourt (Columbia University, New York, and Symplectomorphic, New York) and Andrew Gelman (Columbia University, New York)

Paper:             ‘Graphics for uncertainty’

Authors:         Adrian W. Bowman (University of Glasgow)

PDFs and supplementary files of these papers from StatsLife and the RSS website. As usual, contributions can be sent in writing, with a deadline of September 19.

the end of the Series B’log…

Posted in Books, Statistics, University life with tags , , , , on September 22, 2017 by xi'an

Today is the last and final day of Series B’log as David Dunson, Piotr Fryzlewicz and myself have decided to stop the experiment, faute de combattants. (As we say in French.) The authors nicely contributed long abstracts of their papers, for which I am grateful, but with a single exception, no one came out with comments or criticisms, and the idea to turn some Series B papers into discussion papers does not seem to appeal, at least in this format. Maybe the concept will be rekindled in another form in the near future, but for now we let it lay down. So be it!

Series B’log

Posted in Books, Statistics, University life with tags , , , , on May 31, 2017 by xi'an

Since the above announcement in the RSS newsletter a few months ago, about the Series B’log coming to life, I have received exactly zero comments from readers, despite several authors kindly contributing an extended abstract of their paper. And announcements to various societies…

Hence I now seriously wonder at the survival probability of the blog, given this collective lack of interest. It may be that the information did not reach enough people (despite my mentioning its existence on each talk I give abroad). It may be that the blog still sounds like “under construction”, in which case I’d like to hear suggestions to make it look more definitive! But overall I remain fairly pessimistic [even conditional on my Gallic gloom] about our chances of success with this experiment which could have turned every Series B paper into a potential discussion paper!

London snapshot [jatp]

Posted in pictures, Running, Statistics, Travel with tags , , , , , , on April 13, 2017 by xi'an

a somewhat hasty announcement

Posted in Books, Statistics, University life with tags , , , , , on March 13, 2017 by xi'an

When I received the above RSS newsletter on Thursday, I was a bit shocked as I had not planned to make the existence of the Series B’log known to the entire Society. Even though it was already visible and with unrestricted access. The reason being that experimenting with authors and editors was easier without additional email and password exchanges…

Anyway, now that we have jumped that Rubicon, I would more than welcome comments and suggestions to make the blog structure more efficient and readable. I am still confused as to how the front page should look like, because I want to keep the hierarchy of the Journal, i.e., volume/issue/paper, reflected in this structure, rather than piling up comments and authors’ summaries in an haphazard manner. I have started to tag entries by the volume/issue tag, in order to keep some of this hierarchy respected but I would like to also provide all entries related to a given paper without getting into much extra-work. Given that I already have to process most entries through latex2wp in the best scenario.

coauthorship and citation networks

Posted in Books, pictures, R, Statistics, University life with tags , , , , , , , , , on February 21, 2017 by xi'an

cozauthorAs I discovered (!) the Annals of Applied Statistics in my mailbox just prior to taking the local train to Dauphine for the first time in 2017 (!), I started reading it on the way, but did not get any further than the first discussion paper by Pengsheng Ji and Jiashun Jin on coauthorship and citation networks for statisticians. I found the whole exercise intriguing, I must confess, with little to support a whole discussion on the topic. I may have read the paper too superficially as a métro pastime, but to me it sounded more like a post-hoc analysis than a statistical exercise, something like looking at the network or rather at the output of a software representing networks and making sense of clumps and sub-networks a posteriori. (In a way this reminded of my first SAS project at school, on the patterns of vacations in France. It was in 1983 on pinched cards. And we spent a while cutting & pasting in a literal sense the 80 column graphs produced by SAS on endless listings.)

It may be that part of the interest in the paper is self-centred. I do not think analysing a similar dataset in another field like deconstructionist philosophy or Korean raku would have attracted the same attention. Looking at the clusters and the names on the pictures is obviously making sense, if more at a curiosity than a scientific level, as I do not think this brings much in terms of ranking and evaluating research (despite what Bernard Silverman suggests in his preface) or understanding collaborations (beyond the fact that people in the same subfield or same active place like Duke tend to collaborate). Speaking of curiosity, I was quite surprised to spot my name in one network and even more to see that I was part of the “High-Dimensional Data Analysis” cluster, rather than of the “Bayes” cluster.  I cannot fathom how I ended up in that theme, as I cannot think of a single paper of mines pertaining to either high dimensions or data analysis [to force the trait just a wee bit!]. Maybe thanks to my joint paper with Peter Mueller. (I tried to check the data itself but cannot trace my own papers in the raw datafiles.)

I also wonder what is the point of looking at solely four major journals in the field, missing for instance most of computational statistics and biostatistics, not to mention machine learning or econometrics. This results in a somewhat narrow niche, if obviously recovering the main authors in the [corresponding] field. Some major players in computational stats still make it to the lists, like Gareth Roberts or Håvard Rue, but under the wrong categorisation of spatial statistics.