## modelling protocol in Nature

Posted in Books, Kids, Statistics, University life with tags , , , , , , , on August 19, 2020 by xi'an

A three-page commentary in a recent issue of Nature is a manifesto for responsible modelling, with among the numerous signatories, Deborah Mayo.  (And Phillip Stark as the only statistician I spotted.) The main theme is that the model is not the real thing, e.g., the map is not the territory. Which as such is hardly debatable. The point of the tribune is that, in the light of the pandemic crisis, a large portion of the general population has discovered that mathematical models were not the truth and that their predictions were to be taken with a few marshes of salt. Either because they were based on faulty or antiquated data, if any. Or because their approximation level was too high to return any reliable figure. A failure to understand the nature of mathematical models reminding me of the 2008 financial crisis and of the bemused question of Liz Windsor and of the muddled response of economists:

“Why did nobody notice it?”

“Your Majesty,” eminent economists replied, “the failure to foresee the timing, extent and severity of the crisis and to head it off, while it had many causes, was principally a failure of the collective imagination of many bright people, both in this country and internationally, to understand the risks to the system as a whole.”

“People got a bit lax … perhaps it is difficult to foresee”

The manifesto calls for open assumptions, sensitivity analysis, uncertainty quantification, wariness of overfitting and structural biases (what is the utility function?), and the inclusion of ignorance acknowledgement as an outcome of the model. Which again sounds completely sound if not necessarily helpful when facing interlocutors asking for point estimates. I also regret that the tribune gives hardly any room to statistics and the model checking tools it had developed, except in mentioning the p-hacking and the false feeling of certainty produced by a p-value. Plus a bizarre mention of a French movement of statactivistes of which I had not heard and which seems connected to a book published in French by three of the signatories.

## MCMC at ICMS (3)

Posted in pictures, Statistics, Travel, University life with tags , , , , , , , , , , , , , , , on April 26, 2012 by xi'an

The intense pace of the two first days of our workshop on MCMC at ICMS had apparently taken an heavy toll on the participants as a part of the audience was missing this morning! Although not as a consequence of the haggis of the previous night at the conference dinner, nor even as a result of the above pace. In fact, the missing participants had opted ahead of time for leaving the workshop early, which is understandable given everyone’s busy schedule, esp. for those attending both Bristol and Edinburgh workshops, however slightly impacting the atmosphere of the final day. (Except for Mark Girolami who most unfortunately suffered such a teeth infection that he had to seek urgent medical assistance yesterday afternoon. Best wishes to Mark for a prompt recovery, say I with a dental appointment tomorrow…!)

$y=\sqrt{1-\beta^2}x_{t-1}+\beta\zeta\quad 0<\beta<1,\zeta\sim\varphi(|\zeta|)$