andrew_gelman_stats andrew_gelman_stats-2010 andrew_gelman_stats-2010-156 knowledge-graph by maker-knowledge-mining
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Introduction: This makes sense: In the land of fiction, it’s the criminal’s modus operandi – his method of entry, his taste for certain jewellery and so forth – that can be used by detectives to identify his handiwork. The reality according to a new analysis of solved burglaries in the Northamptonshire region of England is that these aspects of criminal behaviour are on their own unreliable as identifying markers, most likely because they are dictated by circumstances rather than the criminal’s taste and style. However, the geographical spread and timing of a burglar’s crimes are distinctive, and could help with police investigations. And, as a bonus, more Tourette’s pride! P.S. On yet another unrelated topic from the same blog, I wonder if the researchers in this study are aware that the difference between “significant” and “not significant” is not itself statistically significant .
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1 This makes sense: In the land of fiction, it’s the criminal’s modus operandi – his method of entry, his taste for certain jewellery and so forth – that can be used by detectives to identify his handiwork. [sent-1, score-1.121]
2 The reality according to a new analysis of solved burglaries in the Northamptonshire region of England is that these aspects of criminal behaviour are on their own unreliable as identifying markers, most likely because they are dictated by circumstances rather than the criminal’s taste and style. [sent-2, score-2.22]
3 However, the geographical spread and timing of a burglar’s crimes are distinctive, and could help with police investigations. [sent-3, score-0.794]
4 On yet another unrelated topic from the same blog, I wonder if the researchers in this study are aware that the difference between “significant” and “not significant” is not itself statistically significant . [sent-7, score-1.031]
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same-blog 1 0.99999988 156 andrew gelman stats-2010-07-20-Burglars are local
Introduction: This makes sense: In the land of fiction, it’s the criminal’s modus operandi – his method of entry, his taste for certain jewellery and so forth – that can be used by detectives to identify his handiwork. The reality according to a new analysis of solved burglaries in the Northamptonshire region of England is that these aspects of criminal behaviour are on their own unreliable as identifying markers, most likely because they are dictated by circumstances rather than the criminal’s taste and style. However, the geographical spread and timing of a burglar’s crimes are distinctive, and could help with police investigations. And, as a bonus, more Tourette’s pride! P.S. On yet another unrelated topic from the same blog, I wonder if the researchers in this study are aware that the difference between “significant” and “not significant” is not itself statistically significant .
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Introduction: The title of this post by Sanjay Srivastava illustrates an annoying misconception that’s crept into the (otherwise delightful) recent publicity related to my article with Hal Stern, he difference between “significant” and “not significant” is not itself statistically significant. When people bring this up, they keep referring to the difference between p=0.05 and p=0.06, making the familiar (and correct) point about the arbitrariness of the conventional p-value threshold of 0.05. And, sure, I agree with this, but everybody knows that already. The point Hal and I were making was that even apparently large differences in p-values are not statistically significant. For example, if you have one study with z=2.5 (almost significant at the 1% level!) and another with z=1 (not statistically significant at all, only 1 se from zero!), then their difference has a z of about 1 (again, not statistically significant at all). So it’s not just a comparison of 0.05 vs. 0.06, even a differenc
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Introduction: Washington Post columnist Richard Cohen brings up one of my research topics: In New York City, blacks make up a quarter of the population, yet they represent 78 percent of all shooting suspects — almost all of them young men. We know them from the nightly news. Those statistics represent the justification for New York City’s controversial stop-and-frisk program, which amounts to racial profiling writ large. After all, if young black males are your shooters, then it ought to be young black males whom the police stop and frisk. I have two comments on this. First, my research with Jeff Fagan and Alex Kiss (based on data from the late 1990s, so maybe things have changed) found that the NYPD was stopping blacks and hispanics at a rate higher than their previous arrest rates: To briefly summarize our findings, blacks and Hispanics represented 51% and 33% of the stops while representing only 26% and 24% of the New York City population. Compared with the number of arrests of
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Introduction: I’ve talked about this a bit but it’s never had its own blog entry (until now). Statistically significant findings tend to overestimate the magnitude of effects. This holds in general (because E(|x|) > |E(x)|) but even more so if you restrict to statistically significant results. Here’s an example. Suppose a true effect of theta is unbiasedly estimated by y ~ N (theta, 1). Further suppose that we will only consider statistically significant results, that is, cases in which |y| > 2. The estimate “|y| conditional on |y|>2″ is clearly an overestimate of |theta|. First off, if |theta|<2, the estimate |y| conditional on statistical significance is not only too high in expectation, it's always too high. This is a problem, given that |theta| is in reality probably is less than 2. (The low-hangning fruit have already been picked, remember?) But even if |theta|>2, the estimate |y| conditional on statistical significance will still be too high in expectation. For a discussion o
Introduction: Maggie Fox writes : Brain scans may be able to predict what you will do better than you can yourself . . . They found a way to interpret “real time” brain images to show whether people who viewed messages about using sunscreen would actually use sunscreen during the following week. The scans were more accurate than the volunteers were, Emily Falk and colleagues at the University of California Los Angeles reported in the Journal of Neuroscience. . . . About half the volunteers had correctly predicted whether they would use sunscreen. The research team analyzed and re-analyzed the MRI scans to see if they could find any brain activity that would do better. Activity in one area of the brain, a particular part of the medial prefrontal cortex, provided the best information. “From this region of the brain, we can predict for about three-quarters of the people whether they will increase their use of sunscreen beyond what they say they will do,” Lieberman said. “It is the one re
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Introduction: This makes sense: In the land of fiction, it’s the criminal’s modus operandi – his method of entry, his taste for certain jewellery and so forth – that can be used by detectives to identify his handiwork. The reality according to a new analysis of solved burglaries in the Northamptonshire region of England is that these aspects of criminal behaviour are on their own unreliable as identifying markers, most likely because they are dictated by circumstances rather than the criminal’s taste and style. However, the geographical spread and timing of a burglar’s crimes are distinctive, and could help with police investigations. And, as a bonus, more Tourette’s pride! P.S. On yet another unrelated topic from the same blog, I wonder if the researchers in this study are aware that the difference between “significant” and “not significant” is not itself statistically significant .
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Introduction: The title of this post by Sanjay Srivastava illustrates an annoying misconception that’s crept into the (otherwise delightful) recent publicity related to my article with Hal Stern, he difference between “significant” and “not significant” is not itself statistically significant. When people bring this up, they keep referring to the difference between p=0.05 and p=0.06, making the familiar (and correct) point about the arbitrariness of the conventional p-value threshold of 0.05. And, sure, I agree with this, but everybody knows that already. The point Hal and I were making was that even apparently large differences in p-values are not statistically significant. For example, if you have one study with z=2.5 (almost significant at the 1% level!) and another with z=1 (not statistically significant at all, only 1 se from zero!), then their difference has a z of about 1 (again, not statistically significant at all). So it’s not just a comparison of 0.05 vs. 0.06, even a differenc
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Introduction: False-Positive Psychology: Undisclosed Flexibility in Data Collection and Analysis Allows Presenting Anything as Significant [I]t is unacceptably easy to publish “statistically significant” evidence consistent with any hypothesis. The culprit is a construct we refer to as researcher degrees of freedom. In the course of collecting and analyzing data, researchers have many decisions to make: Should more data be collected? Should some observations be excluded? Which conditions should be combined and which ones compared? Which control variables should be considered? Should specific measures be combined or transformed or both? It is rare, and sometimes impractical, for researchers to make all these decisions beforehand. Rather, it is common (and accepted practice) for researchers to explore various analytic alternatives, to search for a combination that yields “statistical significance,” and to then report only what “worked.” The problem, of course, is that the likelihood of at leas
Introduction: Maggie Fox writes : Brain scans may be able to predict what you will do better than you can yourself . . . They found a way to interpret “real time” brain images to show whether people who viewed messages about using sunscreen would actually use sunscreen during the following week. The scans were more accurate than the volunteers were, Emily Falk and colleagues at the University of California Los Angeles reported in the Journal of Neuroscience. . . . About half the volunteers had correctly predicted whether they would use sunscreen. The research team analyzed and re-analyzed the MRI scans to see if they could find any brain activity that would do better. Activity in one area of the brain, a particular part of the medial prefrontal cortex, provided the best information. “From this region of the brain, we can predict for about three-quarters of the people whether they will increase their use of sunscreen beyond what they say they will do,” Lieberman said. “It is the one re
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Introduction: I’ve talked about this a bit but it’s never had its own blog entry (until now). Statistically significant findings tend to overestimate the magnitude of effects. This holds in general (because E(|x|) > |E(x)|) but even more so if you restrict to statistically significant results. Here’s an example. Suppose a true effect of theta is unbiasedly estimated by y ~ N (theta, 1). Further suppose that we will only consider statistically significant results, that is, cases in which |y| > 2. The estimate “|y| conditional on |y|>2″ is clearly an overestimate of |theta|. First off, if |theta|<2, the estimate |y| conditional on statistical significance is not only too high in expectation, it's always too high. This is a problem, given that |theta| is in reality probably is less than 2. (The low-hangning fruit have already been picked, remember?) But even if |theta|>2, the estimate |y| conditional on statistical significance will still be too high in expectation. For a discussion o
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Introduction: This makes sense: In the land of fiction, it’s the criminal’s modus operandi – his method of entry, his taste for certain jewellery and so forth – that can be used by detectives to identify his handiwork. The reality according to a new analysis of solved burglaries in the Northamptonshire region of England is that these aspects of criminal behaviour are on their own unreliable as identifying markers, most likely because they are dictated by circumstances rather than the criminal’s taste and style. However, the geographical spread and timing of a burglar’s crimes are distinctive, and could help with police investigations. And, as a bonus, more Tourette’s pride! P.S. On yet another unrelated topic from the same blog, I wonder if the researchers in this study are aware that the difference between “significant” and “not significant” is not itself statistically significant .
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