Thursday, May 6, 2010

What probability is about

Just as formal logic is a tool for capturing intuitions about effective ways of reasoning probability is a tool for capturing effective ways of reasoning about uncertainty.  In logic, we are taught to proceed from premises to conclusions. We conclude  that "If every CSE graduate takes the exit exam  before graduating and Emily is a CSE graduate, then Emily must have taken the exam" because this matches the Modus ponens pattern P \to Q, P \vdash Q.  The good thing about this is that if we trust Modus ponens and we believe that we have correctly mapped the English description of the conclusion onto the terms of the formula, we know that the argument is valid. Notice that this claim of validity is not affected by the truth or falsity of the premises. Even if Emily never was a CSE student, or even if some CSE students are in fact able to weasel out of taking the exit exam, the argument is still OK. Not, however, especially useful as a way of working out stuff about Emily: if we aren't sure about the assumptions, we can't be sure about the conclusion either. Aristotle hit on the idea of laying out a taxonomy of plausible ways of reasoning, then thinking, in the abstract, about which of these patterns of reasoning actually deliver valid arguments. This is a wonderful idea, because you can rely on the insights about the patterns of reasoning without having to be concerned about the truth or falsity of particular facts.

In the same way that logic is the study of patterns of true/false reasoning, probability is the study of patterns of reasoning in the face of uncertainty.

Tuesday, April 27, 2010

Why statisticians shouldn't write movie titles

Never Give a Sucker an Asymptotically Even Flip
The Variational Enigma
The Fisher King
Independence Day
Return to Monte Casino
The Man Who Measured the Bank at Monte Carlo
Between 99 and 103 Dalmatians
8.5 +/- 0.2
The Metropolis Method (void where prohibited by law)
Improper Priors go wild on Cancun

Tuesday, April 6, 2010

War reporting

Yesterday Wikileaks  



posted a shocking video taken from an Apache helicopter in Iraq. It

Julian Assange, who founded Wikileaks, was interviewed about this.



. He feels that the soldiers in the helicopter obviously committed a war crime, and that

Plain speaker's guide to "any more" and "anymore:

First here's a rephrasing of what Huddleston and Pullum's epic Cambridge Grammar of English says about "any more" and similar adverbs. The main discussion is on p 710 and following, with other bits on 823 and 831

  1. They are polarity sensitive: this means that there is a difference in acceptability between "She isn't here any more" and "She is here any more". For many speakers, the first is OK, the second not.

  2. The difference between "any more" and "anymore" is a British/American spelling difference.

  3. You can line up "anymore" with "still" and "no longer". They differ in how they work with negation.


My own impressions follow. Most speakers can say :

"She is still here" (i.e. she is here and has been for a while)
"She is still not here" (i.e. we are waiting, and she still hasn't arrived),
"She is not here anymore" ,"She is no longer here" (in both cases, she was here, but now isn't)

Many speakers find: "She is not still here","She is here anymore" awkward. For the first one the intended meaning is the same as the one expressed by "She is no longer here". Some speakers, including me, blow a fuse when confronted with the second one, and don't even understand what it means. For others, "anymore" can be used anywhere that "nowadays" is, with much the same meaning, so "She is here anymore" could be used (if you are, say, in a bar) when the person in question used to avoid the bar but now hangs out there on a regular basis. Similarly "Ice cream is cheap anymore" works for many people, but in my natural dialects, I  would have to either turn it round and say "Ice cream isn't expensive anymore" or punt and say "Ice cream is cheap nowadays".

Unfortunately, linguists have taken to confusing themselves and others by talking about "positive anymore".  If they had called it "nowadays anymore" there would have  been no trouble. These adverbs are neither positive nor negative, just a little fussy about what kind of sentences they like to be wrapped up in. The "nowadays" translation helped me, and is from John Lawler. As he says

Apparently, for users of positive "anymore", "nowadays" doesn't
cut it anymore. Anymore, they use "anymore" instead. Or perhaps
only in certain speech contexts; the definitive sociolinguistic
study remains to be done.


I guess I can forgive him for using the term "positive", because he puts it in quotes and gives an amusing example.

By the way, in Columbus, Ohio. ice cream really is cheap and good at Graeter's and  Jeni's . No ice creams were consumed in the creation of this post, but several area shops are on high alert.

Facebook's de facto terms of use

If you are thinking of collecting and distributing data from social media sites, you should read
Pete Warden's account of how Facebook responded to his activities.. Facebook appears to be keen to exert more control than one would think they are entitled to, and certainly more than is convenient for academics. Nobody knows how this would play out in court… Twitter is looking better than ever as a data source.

Thursday, April 1, 2010

Genuinely funny April Fool article

This one actually made me laugh:


A would-be saboteur arrested today at the Large Hadron Collider in Switzerland made the bizarre claim that he was from the future. Eloi Cole, a strangely dressed young man, said that he had travelled back in time to prevent the LHC from destroying the world.

The LHC successfully collided particles at record force earlier this week, a milestone Mr Cole was attempting to disrupt by stopping supplies of Mountain Dew to the experiment's vending machines.


http://crave.cnet.co.uk/gadgets/0,39029552,49305387,00.htm?s_cid=33

Environmentally concerned spouse

"It felt so good to throw away that Martha Stewart dishwasher liquid"

Context: in our machine, Martha Stewart's green dishwasher liquid may be green, but isn't effective for washing.