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Showing posts with label United States. Show all posts
Showing posts with label United States. Show all posts

Sunday, December 2, 2012

Things to Read, 2nd December

Time for another collection of worthwhile links from elsewhere on the internet.

Science links:
  • Jester at Résonaances has been producing a series of very good informative posts from the frontlines of particle physics: particularly worth reading are this summary of the state of play with the "detection" of dark matter by the Fermi telescope, this explanation on what is and isn't contained in the new Higgs analyses from the LHC, including intriguing information on why some data hasn't yet been updated, and this take on the relevance of the LHCb measurements of Bs meson decay for supersymmetry (which has been the subject of a lot of hype in the popular press).
  • Speaking of the popular press, Time magazine has seen fit to nominate the Higgs boson as one of the candidates for "person of the year" (you can vote for it if you like). As if that weren't ridiculous enough, the accompanying description must surely qualify as one of the worst pieces of science journalism ever: literally every single sentence is wrong. Worth a look — even if you're not a physicist, you might be able to spot the mistakes.
  • I've recently discovered a series of super-slow-motion videos of lightning strikes knocking around on the internet. These are shot at several thousand frames per second, and really show the details of how the charge leaders meander towards the ground before the main secondary stroke follows. Even more interesting are some videos showing lightning travelling upwards, from ground to cloud. Here's a video:

    and here's a popular-level description of the phenomenon.
  • Another particularly cool video I saw some time ago was this one, showing the synchronisation of 32 metronomes placed on a flexible platform:


Other links:
  • This one is part science, part history and part politics. Have you ever wondered what the connection is between prehistoric plankton from the Cretaceous era, and the distribution of votes for Obama? Of course you haven't, but now you can find out anyway. 
  • On a more serious note: one of the striking things about the US election was how completely wrong Republicans and the right-wing were in their predictions of the outcome. Especially so since there were so many people who were able, by simple analysis of the available facts, to arrive at predictions that were much better (Nate Silver, for one). There is lots to be said about this, I suppose. One striking observation, which maybe hasn't been made enough of, is the hope that people realise that if the right-wing media can spout such rubbish (not to say lies) about the polls, perhaps the rest of what they say is rubbish too
  • And following on from that, an interesting article from someone on the right of American politics: The Revenge of the Reality-Based Community.
  • It's not just in the US that facts have a well-known anti-right-wing bias of course. And it's not just US right-wing politicians who dislike them. When economist Jonathan Portes of the National Institute for Economic and Social Research appeared before the UK parliament and explained some fairly elementary economics that happens to contradict the ideology of the Conservative Party, he received thinly veiled threats from MP Jesse Norman (watch; transcript). This drives other economists to express their equally thinly veiled contempt. Norman responds, and Wren-Lewis dismisses him again.
  • And finally, something more cheery: some time ago I posted the story about the dog who climbed a mountain with me in the Himalayas. I thought that dog was pretty awesome, but then I saw this dog, who seems to have done an even harder climb!

    (She does seem to have a protective harness though, which probably gives her an unfair advantage ...)

Saturday, November 10, 2012

Does Nate Silver get his maths wrong?

Although I haven't had much time to write anything new for this blog recently, like most people I know I have of course been paying close attention to the unfolding circus of the US Presidential election. Now that all the action is done and dusted, there is a lot of discussion on the internet about the predictions made by poll aggregators, the best-known of whom is the New York Times blogger and statistician Nate Silver. And although I'm not going to talk about politics, I do want to make a comment about probabilities and the statistics of poll aggregation.

The reason Silver has been in the news so much is because even when a lot of innumerate and possibly partisan journalists were making a huge amount of noise about "Romneymentum" and predicting a landslide Republican victory, Silver calmly analysed the actual polls and stated that the odds continued to favour an Obama victory. For this he attracted an enormous amount of flak in the right-wing press and blogs, and a substantial section of the mainstream media refused to believe him. (See here if you'd like a frequently-updated list of everyone who attacked Silver and ended up looking stupid.) Even on election eve, when Silver gave Obama more than a 90% chance of victory, such impartial websites as the BBC continued to describe the result as being on a "knife-edge".

Of course now that Obama has won, the pendulum has turned the other way, and Silver is being hailed as a mathematical genius, a wizard, a guru and much else besides. This adulation rather ignores the fact that there were several other bloggers and poll aggregators who also predicted an Obama win. Some of these are Sam Wang at the Princeton Election Consortium, Drew Linzer at Votamatic, Pollster at the Huffington Post, Simon Jackman and so on. (To be fair, Silver does have a much more prominent position than the others, being at the New York Times. He did also provide very insightful regular explanations and updates, and some nice interactive graphics to help explore the data, so one can forgive the extra attention given to him.)

But the interesting question is not whether Nate Silver does a better job of predicting elections than, say, Donald Trump. How does he compare with other, equally numerate and mathematically minded poll-aggregating bloggers? And there is really a difference between them: for a large part of October, Silver rated Obama's chances of re-election at only around 65-75%, whereas Sam Wang regularly claimed it was more like a 99% chance. Or have a look at Votamatic, where the predicted median of electoral college votes for Obama has been fairly constant at 332 (the correct number) since July, compared to Silver's prediction of closer to 290 at the same time. You'll also notice, if you play with the graphics at FiveThirtyEight, that the margin of error Silver quoted on his prediction was significantly larger than that the other forecasters gave.

So in summary, Nate Silver made more conservative predictions and was more pessimistic about Obama's re-election chances than his direct competitors. (Why so? As I understand it, Wang and Linzer only include information from published poll data, appropriately weighted for freshness and sample size. Silver included also what he calls "fundamentals" — his estimate of other underlying factors, such as economic data and so on, which might influence the final outcome. Silver's exact model is proprietary, but for an educated guess at how it works, explained in layman's terms, see here.) In the end though, Obama was re-elected, as all the forecasters said he would be. Since the only differences between them lay in exactly how confident they were in their prediction (and also whether they thought he would win Florida ... ), and the election can only be run once, how do you decide whose model is better?

A common argument you may have heard in favour of Silver before Obama's most recent victory is that he correctly predicted 49 out of 50 state results in 2008. Add to that his predictions this year and his tally is now 99 correct out of 100. This is obviously impressive, and clearly you should trust Silver and his maths more than basically every conservative hack who attacked him.

But the problem is that Silver may be too accurate. To put it bluntly, if you say the probability of your prediction being correct is around 70%, you should expect to be wrong 30% of the time, not 1% of the time. So if you predict the right result 99% of the time but quote probabilities of only 70%, you are probably overstating the error bars on your prediction. On the other hand, if someone else says he is 99% sure and is right 99% of the time, his model might be better.

OK, some obvious caveats. It is misleading to count all 50 state predictions as successes for Silver's model. I doubt even Donald Trump would have had trouble predicting Utah would go Republican and New York would go Democrat. In reality, there were only around 10 or 11 states that were at all competitive in each election cycle, so adjusting for that would mean lowering Silver's actual success percentage. Also, his model didn't predict all results with equal confidence — for instance, maybe he gave only a 75% probability for Obama to win Ohio, but a 99% probability for him to win Minnesota.

How should one account for this in quantitatively comparing models? Unsurprisingly, Sam Wang himself suggests a method, which is to assign each prediction a Brier score. This takes the square of the difference between the predicted probability of an event occurring — e.g., 0.75 for a prediction of 75% probability — and the post facto probability (i.e. 1 if it did happen, 0 if it didn't). In the case of multiple predictions (for multiple states), you then average the Brier score for each prediction. Thus the Brier score punishes you for getting a prediction wrong, but it also punishes you for hedging your bets too much, even if you got the end result right. Getting a Brier score of exactly 0 would mean you knew the results in advance, getting a score of 0.25 is equivalent to just guessing randomly (if there are only two possible outcomes).

Have a look at Wang's result tables: it looks as though he did slightly better than Silver in predicting the Presidential race, and much better in predicting the Senate results. As he rather pithily put it,
additional factors used by FiveThirtyEight – “fundamentals” – may have actively hurt the prediction. This suggests that fundamentals are helpful mainly when polls are not available.
Anyway, the point of this post, despite the deliberately provocative title, was not really to attack Nate Silver. Even if he did hedge his bets and overstate his error bars a little, given his very public platform and the consequent stakes, I think that's understandable. The Princeton Election Consortium and Votamatic really don't have the same exposure, so Wang and Linzer would have faced less general opprobrium if they had made a mistake. Also, perhaps more statistics are needed to really make a judgement — though let's not have another election for some time please!

But I think this does illustrate a subtle point about probabilistic predictions that most of the media seem to have missed, so it is worth pointing out. And I feel a little personal guilt for being too pessimistic to believe Sam Wang before last Wednesday!

Saturday, September 8, 2012

Things to Read, 8th September

I have been neglecting this series over the summer, so there are rather a lot of things to highlight today.

Science items:
  • The most interesting piece of physics news over the last few months has been that the wealthy Russian investor and physics fan, Yuri Milner, decided to award a 'Fundamental Physics Prize' to 9 theorists he chose himself. The amount of the award is a staggering $3 million each, wired overnight into the physicist's bank accounts — as many people have pointed out, this makes the prize worth far far more than the Nobel Prize. Suddenly being a physicist almost appears to be a lucrative career choice. The lucky physicists were Nima Arkani-Hamed, Alan Guth, Alexei Kitaev, Maxim Kontsevich, Andrei Linde, Juan Maldacena, Nathan Seiberg, Ashoke Sen and Ed Witten. All big names in theoretical physics.
  • Unsurprisingly, the award of this prize generated a lot of debate. For one thing, it is a huge amount of money. For another, the prizes were awarded basically on the whim of one man, who is not a physicist himself. But perhaps the most controversial thing was reported in the New York Times:
    Unlike the Nobel in physics, the Fundamental Physics Prize can be awarded to scientists whose ideas have not yet been verified by experiments, which often occurs decades later.
    This was picked up on by Peter Woit, who is of course well-known for his dislike of some of the work on string theory that the said physicists are famous for, and was highly critical of the prize, including in an article for an Italian newspaper (English transcript from his blog). I guess most physicists would share his unease with the prize, if perhaps not with string theory itself. It was quite amusing to read Matt Strassler finding himself in a position of agreement with Woit but managing to attack him nevertheless (I get the feeling he really dislikes Woit).
  • Motivated by this discussion, Strassler did put up a very interesting and nuanced personal defence of string theory. Whether you have an opinion on 'The String Wars' or not, you will probably have heard strong criticisms of string theory. This piece will provide some balance.
  • Among the other worthwhile physics discussions were two guest posts at Cosmic Variance: by Terry Rudolph and Douglas Finkbeiner. Both discuss recent research work (in quantum mechanics and searches for dark matter, respectively) and both include interesting little insights into the world of academic publishing.
  • Outside physics, I saw a piece by Dr. Dave Hone in the Guardian science section that includes the lines:
    [...] we have dinosaurs everywhere around us. We have dinosaurs nesting in trees in our gardens, tiny dinosaurs that can hover and fly backwards and feed on nectar, aquatic dinosaurs that live in Antarctica. There are dinosaurs that we eat, we have dinosaurs that can circle the globe without landing, intelligent and puzzle-solving dinosaurs, tall and flightless dinosaurs that can sprint at over 40 miles and hour, and brightly coloured and beautiful dinosaurs almost too numerous to mention.
Other items:
  • Of course the big news over the summer has been the Olympics. It's been impossible to miss the outpourings of national pride in British newspapers at Team GB's medal tally and I have heard also of despondency in countries such as Russia and Australia. But what is the benefit to a nation from this arms race for medals? This was discussed, rather provocatively perhaps given the timing, by Ian Johnson in the New York Review of Books
  • There's been a lot of discussion in the US about the Republican presidential ticket, and in the UK about the dire state of the national economy, now in a longer slump than during the Great Depression. Paul Krugman made the obvious connection, and labelled Chancellor of the Exchequer George Osborne "Britain's Paul Ryan." That post includes a graph that should be shown to everyone who still believes austerity in the recession is the answer to anything:

    One could forgive Krugman for feeling rather frustrated (and perhaps a little smug), because this is pretty much exactly what he predicted back in 2010:
    The British government’s plan is bold, say the pundits — and so it is. But it boldly goes in exactly the wrong direction.
    See also here.
  • Of course some people might remember the 20 "leading economists" who wrote an open letter to The Sunday Times supporting George Osborne's fiscal plans back before the 2010 election. Well, some time ago the New Statesman had the bright idea to go back and ask them if they still stuck by their advice: 9 of the 20 had changed their minds, 10 refused to comment, and only one still agreed with himself.
  • You might wonder what a poor politician is to do: if you have only a degree in History and an ideology as substitutes for genuine competence, you naturally rely on the advice of professional macroeconomists. But when the economists disagree with each other, which ones should you listen to? Jonathan Portes had a post laying out some sensible criteria for judging who to take seriously. Unsurprisingly, people like Krugman, Simon Wren-Lewis and Martin Wolf passed the test, but none of the Sunday Times economists did. Portes notes that not all those who pass his test always agree with each other — but he still always takes them seriously.
  • The New York Review of Books carries a review of two books on the current global and American economic mess by Paul Krugman (End This Depression Now!) and Joseph Stiglitz (The Price of Inequality: How Today's Divided Society Endangers Our Future). What particularly interested me here was learning just how radical Stiglitz appears to be.
  • Incidentally, for those who were interested in the Niall Ferguson episode featured here, John Cassidy in the New Yorker has a longer look at the arguments, and comes to the same conclusions: Ferguson is a lightweight who is being repeatedly knocked to the canvas, and this "isn't a fair fight".
  • And finally, since I'd like to end on an uplifting note, here's a video to cheer us all up.

Wednesday, August 22, 2012

The disgrace of Niall Ferguson

(The content of this post is somewhat beyond the usual remit of this blog.)

A month or so ago, a friend drew my attention to the 2012 BBC Reith Lectures given by Niall Ferguson, a Harvard professor of economic history. This is a particularly prestigious lecture series on BBC Radio 4. Past lecturers have included many famous names, from Bertrand Russell in 1948 to Aung San Suu Kyi in 2011; I would recommend several previous lectures. But on listening to Ferguson, I was so annoyed by the combination of factual errors, non sequiturs, deliberate misrepresentations and schoolboyish debating tactics I heard that I almost composed a long diatribe for this blog to point them all out. In the end I refrained, partly for the sake of my blood pressure.

Now, however, Ferguson is back in the news, for an execrable cover story in Newsweek attacking Barack Obama's economic policy that contains many of the same tactics he employed in his Reith lectures, and I can no longer pass up the opportunity to comment. Luckily the Newsweek story has stirred up such justifiable disdain everywhere that I will be able to outsource much of the detailed commentary and merely provide you with a round-up of the reasons why you should never believe a word Ferguson says or writes.

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