**I**n what appears to be a regular contribution of his to Nature, Daniel Sarewitz recently wrote a “personal take on events” that I find quite reactionary, the more because it comes from an academic. And I wonder why Nature chose to publish his opinion piece. Every other month! The arguments of the author is that basic science should be defunded in favour of “use-inspired” research, “mission oriented” programmes, “societal needs and socially valuable knowledge”… The reason being that it is a better use of public money and that scientists are just another interest group that should not be left to its own device. This is not a new tune, calls to cut down funding fundamental research emerge regularly as an easily found culprit for saving “taxpayer money”, and it is the simplest mean of rejecting a research proposal by blaming its lack of clear applicability. Of course, when looking a bit wider, one can check this piece bemoaning the Democrat inclinations of most scientists. Or that one that science should sometimes give way to religion. With the definitive argument that, for most people, the maths behind scientific models are so complex that they must turn to an act of faith… Yes, I do wonder at Nature providing Sarewitz with such a wide-ranging tribune.

## Archive for Philosophy of Science

## the “myth of the miracle machine”

Posted in Books, University life with tags Arizona, conservatism, funding, Nature, Philosophy of Science, religion, Republicans, US politics on September 13, 2017 by xi'an## fiducial on a string

Posted in Books, pictures, Statistics, Travel, University life with tags Bayesian Fiducial & Frequentist Conference, fiducial inference, Harvard University, Norway, NTU, Philosophy of Science, Teddy Seidenfeld on June 26, 2017 by xi'an**A** very short note in arXiv today by Gunnar Taraldsen and Bo Henry Lindqvist (NTU, Norway). With the above title. I find the note close to unreadable, I must say, as the notations are not all or well- defined. The problem starts from Teddy Seidenfeld [whom I met in Harvard around Dutch book arguments] arguing about the lack of unicity of fiducial distributions in a relatively simple setting. Actually the note is also inspired from Bayes, Fiducial and Frequentist, and comments from Teddy, a talk I apparently missed by taking a flight back home too early!

What I find surprising in this note is that the “fiducial on a string” is a conditional distribution on the parameter space restricted to a curve, derived from the original fiducial distribution by a conditioning argument. Except that since the conditioning is on a set of measure zero, this conditional is not only not-unique, but it is completely undefined and arbitrary, since changing it does not modify the properties of the joint distribution.

## objective and subjective RSS Read Paper next week

Posted in Books, pictures, Statistics, Travel, University life, Wines with tags Andrew Gelman, Christian Hennig, discussion paper, England, frequentist inference, London, objective Bayes, objectivism, Philosophy of Science, Read paper, Royal Statistical Society, RSS, Series A, subjective versus objective Bayes, subjectivity on April 5, 2017 by xi'an**A**ndrew Gelman and Christian Hennig will give a Read Paper presentation next Wednesday, April 12, 5pm, at the Royal Statistical Society, London, on their paper “Beyond subjective and objective in statistics“. Which I hope to attend and else to write a discussion. Since the discussion (to published in Series A) is open to everyone, I strongly encourage ‘Og’s readers to take a look at the paper and the “radical” views therein to hopefully contribute to this discussion. Either as a written discussion or as comments on this very post.

## Fourth Bayesian, Fiducial, and Frequentist Conference

Posted in Books, pictures, Statistics, Travel, University life, Wines with tags Bayesian Analysis, Cambridge, Error-Statistical philosophy, foundations, Harvard University, Philosophy of Science, snow, Statistics done wrong on March 29, 2017 by xi'an**N**ext May 1-3, I will attend the 4th Bayesian, Fiducial and Frequentist Conference at Harvard University (hopefully not under snow at that time of year), which is a meeting between philosophers and statisticians about foundational thinking in statistics and inference under uncertainty. This should be fun! (Registration is now open.)

## sleeping beauty

Posted in Books, Kids, Statistics with tags ABC, Bayesian foundations, credence, decision theory, groundhog day, Harold Jeffreys, logic journal of the IGPL, Philosophy of Science, Shahrazad, sleeping beauty paradox on December 24, 2016 by xi'an**T**hrough X validated, W. Huber made me aware of this probability paradox [or para-paradox] of which I had never heard before. One of many guises of this paradox goes as follows:

Shahrazad is put to sleep on Sunday night. Depending on the hidden toss of a fair coin, she is awaken either once (Heads) or twice (Tails). After each awakening, she gets back to sleep and forget that awakening. When awakened, what should her probability of Heads be?

My first reaction is to argue that Shahrazad does not gain information between the time she goes to sleep when the coin is fair and the time(s) she is awaken, apart from being awaken, since she does not know how many times she has been awaken, so the probability of Heads remains ½. However, when thinking more about it on my bike ride to work, I thought of the problem as a decision theory or betting problem, which makes ⅓ the optimal answer.

I then read [if not the huge literature] a rather extensive analysis of the paradox by Ciweski, Kadane, Schervish, Seidenfeld, and Stern (CKS³), which concludes at roughly the same thing, namely that, when Monday is completely exchangeable with Tuesday, meaning that no event can bring any indication to Shahrazad of which day it is, the posterior probability of Heads does not change (Corollary 1) but that a fair betting strategy is p=1/3, with the somewhat confusing remark by CKS³ that this may differ from her credence. But then what is the point of the experiment? Or what is the meaning of *credence*? If Shahrazad is asked for an answer, there must be a utility or a penalty involved otherwise she could as well reply with a probability of p=-3.14 or p=10.56… This makes for another ill-defined aspect of the “paradox”.

Another remark about this ill-posed nature of the experiment is that, when imagining running an ABC experiment, I could only come with one where the fair coin is thrown (Heads or Tails) and a day (Monday or Tuesday) is chosen at random. Then every proposal (Heads or Tails) is accepted as an awakening, hence the posterior on Heads is the uniform prior. The same would not occurs if we consider the pair of awakenings under Tails as two occurrences of (p,E), but this does not sound (as) correct since Shahrazad only knows of one E: to paraphrase Jeffreys, this is an unobservable result that may have not *occurred*. (Or in other words, Bayesian learning is not possible on Groundhog Day!)

## Le bayésianisme aujourd’hui

Posted in Books, Statistics with tags Bayesianism, book chapter, epistemology, foundations, France, French book, game theory, Philosophy of Science on September 19, 2016 by xi'an**A** few years ago, I was asked by Isabelle Drouet to contribute a chapter to a multi-disciplinary book on the Bayesian paradigm, book that is now soon to appear. In French. It has this rather ugly title of *Bayesianism today*. Not that I had hear of *Bayesianism* or *bayésianime* previously. There are chapters on the Bayesian notion(s) of probability, game theory, statistics, on applications, and on the (potentially) Bayesian structure of human intelligence. Most of it is thus outside statistics, but I will certainly read through it when I receive my copy.

## on de Finetti’s instrumentalist philosophy of probability

Posted in Books, Statistics, Travel, University life with tags Bayesian foundations, behaviorism, Bruno de Finetti, Paris, philosophy, Philosophy of Science, realism, subjective probability, subjective versus objective Bayes on January 5, 2016 by xi'an**O**n Wednesday January 6, there is a conference in Paris [10:30, IHPST, 13, rue du Four, Paris 6] by Joseph Berkovitz (University of Toronto) on the philosophy of probability of Bruno de Finetti. Too bad this is during MCMSkv!

De Finetti is one of the founding fathers of the modern theory of subjective probability, where probabilities are coherent degrees of belief. De Finetti held that probabilities are inherently subjective and he argued that none of the objective interpretations of probability makes sense. While his theory has been influential in science and philosophy, it has encountered various objections. In particular, it has been argued that de Finetti’s concept of probability is too permissive, licensing degrees of belief that we would normally call imprudent. Further, de Finetti is commonly conceived as giving an operational, behaviorist definition of degrees of belief and accordingly of probability. Thus, the theory is said to inherit the difficulties embodied in operationalism and behaviorism. We argue that these and some other objections to de Finetti’s theory are unfounded as they overlook various central aspects of de Finetti’s philosophy of probability. We then propose a new interpretation of de Finetti’s theory that highlights these central aspects and explains how they are an integral part of de Finetti’s instrumentalist philosophy of probability. Building on this interpretation of de Finetti’s theory, we draw some lessons for the realist-instrumentalist controversy about the nature of science.