Have you ever been taught the point about correlation and causation?

Without blinking at the contradiction, the prime minister could boast that crime is down by a third, violent crime by 40%. And yet he boasted of the steep rise in prison numbers, up from 60,000 in softie Tory times to more than 80,000 now, and 96,000 soon – presumably regardless of future crime rates.

Correlation is when we note that two things are moving in tandem. However, we don\’t know whether in fact they are linked. It could be that they are not (global warming coinciding with there being fewer priates is one example), it could be that they are both the symptom of some other matter taking place or it could be that the movement in one of the things being studied is the cause of the other thing. We might point to the correlation between electricty blackouts and a boom in births 9 months later as an example of cause and effect….our causation if you wish.

Now, I don\’t insist that there is indeed causation in those crime numbers. It could indeed be simple correlation. But it\’s difficult to call it a "contradiction" unless we explore whether there is in fact some causation going on here.

More people are going to jail, crime is falling. You know, there is in fact an argument that could be made there to show some causation.

No?

Of course, no truly wonderful Polly column could be complete without a mangling of statistics to add to a failure of logic:

In London, he says, murder has declined slightly – from 2.6% per 100,000 people in 2000 to 2.2% in 2007.

There\’s a disturbing sense there that Polly doesn\’t in fact understand percentages. 2.6% means 2.6 per hundred…..that\’s what percentage means. Murder statistics (in order to get away from using 0.026 %) are expressed as a number per hundred thousand. The way she\’s presented them there we\’ve actually got a murder rate of 2,600 people per hundred thousand people….something like the level of deaths in frontline troops in a bloody war (erm, roughly 100,000 in the British Army, some 100 deaths so far in Afghanistan and Iraq……yes, a bloody war).

Well done Polly!

10 thoughts on “Polly Dear?”

  1. It is shameful, but you’re not right on what it means – the way she’s presented it is 2.2% per 100,000 which means 0.022 per 100,000, which would be about 0.1 murders a year in London.

    Tim adds: Biter bit, eh? Fun when that happens.

  2. Actually that can’t be right either – she’s divided it by 100, so her figures must imply about 1 murder a year in London.

  3. This is typical of the Gruaniad and hte lefty press. Mangle the figures so much that not even someone with a mathematical fucking clue can work out what the fuck they are talking about. Polly the daft bitch should be on income support not paid 5x the national average.

  4. Absolutely useless (and a waste of time) to talk of such things, even to notice such things, and, beyond that, to pay any attention whatever to such matters.

    As Leary said, “The medium is the message.” He was trying to enlighten people who were, presumably, already quite aware that the message was the medium. It seems he overestimated his audience, who lapped it up anyway because it sounded like good, solid, hallucinatory nonsense.

  5. TW

    She failed her 11+, went to Holland Park Comprehensive and flunked out of Oxford – and you expect her to understand percentages. Blimey, I never thought of you as an optimist!

  6. Gene Berman wrote:

    ‘As Leary said, “The medium is the message.” He was trying to enlighten people who were, presumably, already quite aware that the message was the medium. It seems he overestimated his audience, who lapped it up anyway because it sounded like good, solid, hallucinatory nonsense.’

    Except that it was Marshall McLuhan.

    llater,

    llamas

  7. I note the reports that global temperature hasn’t risen in line with various predictions from the green lobby. I also note increased reporting of increasing pirate activity (though I have no figures to back this up, just the impression I get from keeping half an ear on the news). Just saying…

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