## understanding elections through statistics [book review]

Posted in Books, Kids, R, Statistics, Travel with tags , , , , , , , , , , , , , , , , , , , , , , , , on October 12, 2020 by xi'an

A book to read most urgently if hoping to take an informed decision by 03 November! Written by a political scientist cum statistician, Ole Forsberg. (If you were thinking of another political scientist cum statistician, he wrote red state blue state a while ago! And is currently forecasting the outcome of the November election for The Economist.)

“I believe [omitting educational level] was the main reason the [Brexit] polls were wrong.”

The first part of the book is about the statistical analysis of opinion polls (assuming their outcome is given, rather than designing them in the first place). And starting with the Scottish independence referendum of 2014. The first chapter covering the cartoon case of simple sampling from a population, with or without replacement, Bayes and non-Bayes. In somewhat too much detail imho given that this is an unrealistic description of poll outcomes. The second chapter expands to stratified sampling (with confusing title [Polling 399] and entry, since it discusses repeated polls that are not processed in said chapter). Mentioning the famous New York Times experiment where five groups of pollsters analysed the same data, making different decisions in adjusting the sample and identifying likely voters, and coming out with a range of five points in the percentage. Starting to get a wee bit more advanced when designing priors for the population proportions. But still studying a weighted average of the voting intentions for each category. Chapter three reaches the challenging task of combining polls, with a 2017 (South) Korea presidential election as an illustration, involving five polls. It includes a solution to handling older polls by proposing a simple linear regression against time. Chapter 4 sums up the challenges of real-life polling by examining the disastrous 2016 Brexit referendum in the UK. Exposing for instance the complicated biases resulting from polling by phone or on-line. The part that weights polling institutes according to quality does not provide any quantitative detail. (And also a weird averaging between the levels of “support for Brexit” and “maybe-support for Brexit”, see Fig. 4.5!) Concluding as quoted above that missing the educational stratification was the cause for missing the shock wave of referendum day is a possible explanation, but the massive difference in turnover between the age groups, itself possibly induced by the reassuring figures of the published polls and predictions, certainly played a role in missing the (terrible) outcome.

“The fabricated results conformed to Benford’s law on first digits, but failed to obey Benford’s law on second digits.” Wikipedia

The second part of this 200 page book is about election analysis, towards testing for fraud. Hence involving the ubiquitous Benford law. Although applied to the leading digit which I do not think should necessarily follow Benford law due to both the varying sizes and the non-uniform political inclinations of the voting districts (of which there are 39 for the 2009 presidential Afghan election illustration, although the book sticks at 34 (p.106)). My impression was that instead lesser digits should be tested. Chapter 4 actually supports the use of the generalised Benford distribution that accounts for differences in turnouts between the electoral districts. But it cannot come up with a real-life election where the B test points out a discrepancy (and hence a potential fraud). Concluding with the author’s doubt [repeated from his PhD thesis] that these Benford tests “are specious at best”, which makes me wonder why spending 20 pages on the topic. The following chapter thus considers other methods, checking for differential [i.e., not-at-random] invalidation by linear and generalised linear regression on the supporting rate in the district. Once again concluding at no evidence of such fraud when analysing the 2010 Côte d’Ivoire elections (that led to civil war). With an extension in Chapter 7 to an account for spatial correlation. The book concludes with an analysis of the Sri Lankan presidential elections between 1994 and 2019, with conclusions of significant differential invalidation in almost every election (even those not including Tamil provinces from the North).

R code is provided and discussed within the text. Some simple mathematical derivations are found, albeit with a huge dose of warnings (“math-heavy”, “harsh beauty”) and excuses (“feel free to skim”, “the math is entirely optional”). Often, one wonders at the relevance of said derivations for the intended audience and the overall purpose of the book. Nonetheless, it provides an interesting entry on (relatively simple) models applied to election data and could certainly be used as an original textbook on modelling aggregated count data, in particular as it should spark the interest of (some) students.

[Disclaimer about potential self-plagiarism: this post or an edited version will eventually appear in my Books Review section in CHANCE.]

## better together?

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

Yesterday came out on arXiv a joint paper by Pierre Jacob, Lawrence Murray, Chris Holmes and myself, Better together? Statistical learning in models made of modules, paper that was conceived during the MCMski meeting in Chamonix, 2014! Indeed it is mostly due to Martyn Plummer‘s talk at this meeting about the cut issue that we started to work on this topic at the fringes of the [standard] Bayesian world. Fringes because a standard Bayesian approach to the problem would always lead to use the entire dataset and the entire model to infer about a parameter of interest. [Disclaimer: the use of the very slogan of the anti-secessionists during the Scottish Independence Referendum of 2014 in our title is by no means a measure of support of their position!] Comments and suggested applications most welcomed!

The setting of the paper is inspired by realistic situations where a model is made of several modules, connected within a graphical model that represents the statistical dependencies, each relating to a specific data modality. In a standard Bayesian analysis, given data, a conventional statistical update then allows for coherent uncertainty quantification and information propagation through and across the modules. However, misspecification of or even massive uncertainty about any module in the graph can contaminate the estimate and update of parameters of other modules, often in unpredictable ways. Particularly so when certain modules are trusted more than others. Hence the appearance of cut models, where practitioners  prefer skipping the full model and limit the information propagation between these modules, for example by restricting propagation to only one direction along the edges of the graph. (Which is sometimes represented as a diode on the edge.) The paper investigates in which situations and under which formalism such modular approaches can outperform the full model approach in misspecified settings. By developing the appropriate decision-theoretic framework. Meaning we can choose between [several] modular and full-model approaches.

## Scottish polls…

Posted in pictures, Statistics, Travel with tags , , , , , , , , on September 11, 2014 by xi'an

As much as I love Scotland, or because of it, I would not dream of suggesting to Scots that one side of the referendum sounds better than the other. However, I am rather annoyed at the yoyo-like reactions to the successive polls about the result, because, just like during the US elections, each poll is analysed separately rather than being pooled with the earlier ones in a reasonable meta-analysis… Where is Nate Silver when we need him?!

## Saints of the Shadow Bible [book review]

Posted in Books, Travel with tags , , , , , on June 14, 2014 by xi'an

The saints of the shadow Bible following me
From bar to bar to eternity’
Jackie Leven

For once, I read my Rankin in Edinburgh, the very place where it takes place! (Somewhere in the book, Rebus acknowledge he never left Scotland. Which does not sound coherent with trips to London in earlier books… Like Tooth and Nails.) It makes the lecture much more complete, as I could picture some of the places and partly follow Rebus whereabouts within the town… The title of the book is taken from a song of Jackie Leven, a reminder that music is always an essential element in Rankin’s book, as Rebus’ tastes seem to mimic Rankin’s (or vice-versa). A definitely great title… And great cover.

Saints of the Shadow (Bible) is as usual always in tune with the current events in Scotland, from the campaigns for and against independence, to the roadwork for the new tram (which opened two days prior to my arrival in the city). Reminding me of Set in Darkness, set around the building of the then new Scottish parliament. This book is a good serving of Rebus, albeit in a sort of schadenfreunde way, as the (DI demoted to DS) Rebus is irresistibly getting close to retirement, cannot fight or drink so much or even impose his views upon his colleagues, even the most inclined towards him… So (spoiler!) the fight between Rebus and Fox, forced to work together, that I was expecting does not really take place. On the opposite, the earlier attempts of Fox to frame Rebus for his “bad-cop” attitude have vanished and (re-spoiler!) Rebus is central to framing some of his earliest colleagues from Summerhall, even though the book maintains the ambiguity for a long while. As often in detective stories, too many coincidences mar the credibility of the story, which is centred around a few characters and with much less of a societal or political framework than in earlier volumes. Maybe the most interesting character in Saints of the Shadow (Bible) is Siobhan Clarke, as she is growing in stature and authority, breaking the close partnership with Rebus while preserving the deep friendship. (As mentioned in the previous review, I do think Rankin should “finish” Rebus’ cycle and move to another theme and style, but, provisional on this, an enjoyable read completing “the” Scottish experience!))

## standing in another man’s grave

Posted in Books, Mountains, Travel with tags , , , , , , on July 13, 2013 by xi'an

“Just another night when he would not quite make it as far as the bedroom.” Standing in another man’s grave

Rebus is back indeed! When my friend Arnaud told me there was a new Rebus, I could not believe it: I thought Rankin had stopped the series with Rebus’ retirement, and one of the best possible endings (Rebus resuscitating his nemesis, Cafferty, and the superb title of Exit Music) to the series. Now, a new novel has appeared, Standing in another man’s grave, signifying Rebus return on the literary scene (and on the Scottish sleuthing scene as well).

“It’s an odd little country, this, isn’t it? I just mean it’s hard to fathom sometimes. I’ve lived here most of my life and I still don’t understand the place.” Standing in another man’s grave

So, a few years after his retirement (and a few years after the ‘last’ novel), Rebus reappears, as a civil assistant to a jeopardised cold case unit in Edinburgh. Unsurprisingly, Rebus cannot stay put and starts participating in a police investigation about the current disappearance of a young girl. With a possible link with earlier disappearances along the A9 road from Perth to Inverness… (A road with a surprising number of Scotch distilleries along the way, but this is a false trail!)

“A nation of 5 million huddled together as if cowed by the elements and the immensity of the landscape surrounding them, clinging to notions of community and shared history.” Standing in another man’s grave

Pretty soon, Rebus takes over the enquiry and without much backup (except from his former colleague Siobhan) figures out most of the clues leading to the thread common to those young girl disappearances. Pushing towards the resolution with means as grey and borderline as usual. Since part of the book is about Rebus trying to reapply for police work thanks to a new law and the Complaints inspector Malcom Fox is trying to prevent this, the next book (as there will be a next book!) may see Rebus in more trouble.

“Rebus began to wonder if he’d ever been further from a pub in his life.” Standing in another man’s grave

This is Rebus’ Rankin back to life and still… I had the definitive impression that Rebus had gotten much older than the few years since his “retirement”. The story starts as if he had lost all contact with former colleagues and only kept in touch with retirees and dead policemen… Even the early dialogues with Siobhan sound contrived. This may actually be intentional. The story itself has nice sides (like the use of Twitter and Facebook by young officers or the elimination of the catalyst case that started the whole story), but the resolution requires too much of a suspension of disbelief. Too many drinks. Too much driving (even though all those names of towns reminded me of places I visited or wanted to visit in Scotland). Nonetheless enjoyable and a page-turner and paving the way to The Saints of the Shadow Bible… With Scottish independence looming in the back!