andrew_gelman_stats andrew_gelman_stats-2011 andrew_gelman_stats-2011-563 knowledge-graph by maker-knowledge-mining
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Introduction: Mike Cohen writes: The recent events in Egypt raise an interesting statistical question. It is of course common for news stations like CNN to interview various officials and policy experts to find out what is likely to happen next. The obvious response of people like us is why ask such people when they didn’t foresee a month ago that these dynamic events were about to happen. One would instead like to hear from those experts that did predict that something was about to happen in Tunisia, and Egypt, and Jordan, and maybe Yemen, etc. Well, are there such people? My friend Bob Burton says that of course one can find such people in the sense that they made such predictions, but that is like finding counties that have voted for the President in the last five elections, big deal, or psychics that predicted the last assassination, again big deal. There is a good deal of truth in that. However, it seems like we do a little better. There are two points to make. First, there is an i
sentIndex sentText sentNum sentScore
1 Mike Cohen writes: The recent events in Egypt raise an interesting statistical question. [sent-1, score-0.122]
2 It is of course common for news stations like CNN to interview various officials and policy experts to find out what is likely to happen next. [sent-2, score-0.636]
3 The obvious response of people like us is why ask such people when they didn’t foresee a month ago that these dynamic events were about to happen. [sent-3, score-0.312]
4 One would instead like to hear from those experts that did predict that something was about to happen in Tunisia, and Egypt, and Jordan, and maybe Yemen, etc. [sent-4, score-0.476]
5 My friend Bob Burton says that of course one can find such people in the sense that they made such predictions, but that is like finding counties that have voted for the President in the last five elections, big deal, or psychics that predicted the last assassination, again big deal. [sent-6, score-0.345]
6 First, there is an information theory aspect to how impressed we should be by predictions that are made. [sent-10, score-0.428]
7 In the following I am glossing over a very important point, which is how specific the predictions are, and that is worth thinking a lot about. [sent-11, score-0.395]
8 But speaking loosely, for a dichotomous question with both sides close to equal a priori, making a prediction that turns out to be correct is no big deal. [sent-12, score-0.457]
9 But predicting the date and manner in which some political event would occur, such as a change in government well in advance, when the general a priori view was that nothing was going on, would be extremely impressive. [sent-13, score-0.473]
10 So question one is can one measure how impressive a prediction is, to help us understand who our experts really are, and what experts are just guessing well? [sent-14, score-0.641]
11 Second, does Efron’s work 40 years ago on assessing whether Bode’s Law has a physical basis relate to this question? [sent-15, score-0.161]
12 I replied as follows: My quick thought is that any expert forecasts should be evaluated not in a vacuum but in the context of their qualitative models. [sent-18, score-0.333]
13 To which Cohen pointed out that an expert could predict that something was going to happen without having an explicit theory that they were operating from and that would still be of interest, though less so, than if they had put forward how they arrived at such predictions. [sent-20, score-0.78]
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same-blog 1 1.0000001 563 andrew gelman stats-2011-02-07-Evaluating predictions of political events
Introduction: Mike Cohen writes: The recent events in Egypt raise an interesting statistical question. It is of course common for news stations like CNN to interview various officials and policy experts to find out what is likely to happen next. The obvious response of people like us is why ask such people when they didn’t foresee a month ago that these dynamic events were about to happen. One would instead like to hear from those experts that did predict that something was about to happen in Tunisia, and Egypt, and Jordan, and maybe Yemen, etc. Well, are there such people? My friend Bob Burton says that of course one can find such people in the sense that they made such predictions, but that is like finding counties that have voted for the President in the last five elections, big deal, or psychics that predicted the last assassination, again big deal. There is a good deal of truth in that. However, it seems like we do a little better. There are two points to make. First, there is an i
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Introduction: Phil Plait writes : Earth May Have Been Hit by a Cosmic Blast 1200 Years Ago . . . this is nothing to panic about. If it happened at all, it was a long time ago, and unlikely to happen again for hundreds of thousands of years. This left me confused. If it really did happen 1200 years ago, basic statistics would suggest it would occur approximately once every 1200 years or so (within half an order of magnitude). So where does “hundreds of thousands of years” come from? I emailed astronomer David Hogg to see if I was missing something here, and he replied: Yeah, if we think this hit us 1200 years ago, we should imagine that this happens every few thousand years at least. Now that said, if there are *other* reasons for thinking it is exceedingly rare, then that would be a strong a priori argument against believing in the result. So you should either believe that it didn’t happen 1200 years ago, or else you should believe it will happen again in the next few thousan
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Introduction: An interview with me from 2012 : You’re a statistician and wrote a book, Red State, Blue State, Rich State, Poor State , looking at why Americans vote the way they do. In an election year I think it would be a good time to revisit that question, not just for people in the US, but anyone around the world who wants to understand the realities – rather than the stereotypes – of how Americans vote. I regret the title I gave my book. I was too greedy. I wanted it to be an airport bestseller because I figured there were millions of people who are interested in politics and some subset of them are always looking at the statistics. It’s got a very grabby title and as a result people underestimated the content. They thought it was a popularisation of my work, or, at best, an expansion of an article we’d written. But it had tons of original material. If I’d given it a more serious, political science-y title, then all sorts of people would have wanted to read it, because they would
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Introduction: David Hogg writes: My (now deceased) collaborator and guru in all things inference, Sam Roweis, used to emphasize to me that we should evaluate models in the data space — not the parameter space — because models are always effectively “effective” and not really, fundamentally true. Or, in other words, models should be compared in the space of their predictions, not in the space of their parameters (the parameters didn’t really “exist” at all for Sam). In that spirit, when we estimate the effectiveness of a MCMC method or tuning — by autocorrelation time or ESJD or anything else — shouldn’t we be looking at the changes in the model predictions over time, rather than the changes in the parameters over time? That is, the autocorrelation time should be the autocorrelation time in what the model (at the walker position) predicts for the data, and the ESJD should be the expected squared jump distance in what the model predicts for the data? This might resolve the concern I expressed a
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Introduction: Mike Cohen writes: The recent events in Egypt raise an interesting statistical question. It is of course common for news stations like CNN to interview various officials and policy experts to find out what is likely to happen next. The obvious response of people like us is why ask such people when they didn’t foresee a month ago that these dynamic events were about to happen. One would instead like to hear from those experts that did predict that something was about to happen in Tunisia, and Egypt, and Jordan, and maybe Yemen, etc. Well, are there such people? My friend Bob Burton says that of course one can find such people in the sense that they made such predictions, but that is like finding counties that have voted for the President in the last five elections, big deal, or psychics that predicted the last assassination, again big deal. There is a good deal of truth in that. However, it seems like we do a little better. There are two points to make. First, there is an i
Introduction: A few months ago, I blogged on John Gottman, a psychologist whose headline-grabbing research on marriages (he got himself featured in Blink with a claim that he could predict with 83 percent accuracy whether a couple would be divorced—after meeting with them for 15 minutes!) was recently debunked in a book by Laurie Abraham. The question I raised was: how could someone who was evidently so intelligent and accomplished—Gottman, that is—get things so wrong? My brief conclusion was that once you have some success, I guess there’s not much of a motivation to change your ways. Also, I could well believe that, for all its flaws, Gottman’s work is better than much of the other research out there on marriages. There’s still the question of how this stuff gets published in scientific journals. I haven’t looked at Gottman’s articles in detail and so don’t really have thoughts on that one. Anyway, I recently corresponded with a mathematician who had heard of Gottman’s research and wrote
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Introduction: After hearing a few times about the divorce predictions of researchers John Gottman and James Murray (work that was featured in Blink with a claim that they could predict with 83 percent accuracy whether a couple would be divorced–after meeting with them for 15 minutes) and feeling some skepticism , I decided to do the Lord’s work and amend Gottman’s wikipedia entry, which had a paragraph saying: Gottman found his methodology predicts with 90% accuracy which newlywed couples will remain married and which will divorce four to six years later. It is also 81% percent accurate in predicting which marriages will survive after seven to nine years. I added the following: Gottman’s claim of 81% or 90% accuracy is misleading, however, because the accuracy is measured only after fitting a model to his data. There is no evidence that he can predict the outcome of a marriage with high accuracy in advance. As Laurie Abraham writes, “For the 1998 study, which focused on videotapes of 57
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Introduction: Alex Braunstein writes about Klout, a company which measures Twitter/Facebook influence: As a Ph D statistician and search quality engineer, I [Braunstein] know a lot about how to properly measure things. In the past few months I’ve become an active Twitter user and very interested in measuring the influence of individuals. Klout provides a way to measure influence on Twitter using a score also called Klout. The range is 0 to 100. Light users score below 20, regular users around 30, and celebrities start around 75. Naturally, I was intrigued by the Klout measurement, but a careful analysis led to some serious issues with the score. . . . Braunstein continues with some comparisons of different twitter-users and how their Klout scores don’t make much sense. I don’t really see the point of the Klout scores in the first place: I guess they’re supposed to be a quick measure to use in pricing advertising? Whatever, I don’t really care. What did interest me was a remark on Brauns
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Introduction: I read this story by Adrian Chen on Gawker (yeah, yeah, so sue me): Why That ‘NASA Discovers Alien Life’ Story Is Bullshit Fox News has a super-exciting article today: “Exclusive: NASA Scientist claims Evidence of Alien Life on Meteorite.” OMG, aliens exist! Except this NASA scientist has been claiming to have evidence of alien life on meteorites for years. Chen continues with a quote from the Fox News item: [NASA scientist Richard B. Hoover] gave FoxNews.com early access to the out-of-this-world research, published late Friday evening in the March edition of the Journal of Cosmology. In it, Hoover describes the latest findings in his study of an extremely rare class of meteorites, called CI1 carbonaceous chondrites — only nine such meteorites are known to exist on Earth. . . . The bad news is that Hoover reported this same sort of finding in various low-rent venues for several years. Replication, huh? Chen also helpfully points us to the website of the Journal
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