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Polly Toynbee recently wrote on the relationship between income inequality and the prevalence of obesity (more inequality leads to more obesity, she claims). Naturally this has provoked the usual ignorant rebuttals from various corners of the web. Matthew Turner lists a few of these and points out that, whatever the merits or otherwise of Toynbee's piece -- frankly I have better things to do than read it, or the rebuttals, in any detail -- if you plot the prevalence of obesity against the Gini coefficient of income inequality for a bunch of OECD countries, you do indeed get a (weak) positive correlation.
Now, there are two important things to say about this. One is that the various countries of the OECD have substantially different cultures, and this is the sort of thing which is likely to influence the prevalence of obesity. Another is that different countries have widely differing populations, wheras the only sensible causal argument that could be made here is that people who live in unequal societies are (for some reason) more likely to be obese than those who live in more equal ones. On that basis, we should be looking at the data weighted by the populations of the various countries; but if you do this the results are dominated by the appearance of the US (very unequal, very obese, and very populous) and Japan (not very unequal, not very obese, quite populous).
One way around this is to look at obesity within the United States instead. It's true that there is cultural variation within the United States, but presumably it's less important than among the OECD countries; and a wide distribution of populations between the different states (which are the unit over which population, obesity and income data are most conveniently available), but it's not so skewed as the distribution of population in the OECD. Anyway, we can get somewhere with this:
The best-fit line has a slope of 11.45±11.33 (that's a standard error, not a confidence interval). So this provides very weak evidence for positive correlation (that is, the result is compatible with the two variables being uncorrelated and their being weakly correlated, but not with their being negatively correlated or strongly positively correlated). Any relationship in these data is far-from-striking.
Can we conclude anything useful from this? Not a lot, frankly, beyond that you shouldn't assume that somebody else's statistics are right just because they disagree with Polly Toynbee. I'm suspicious of this sort of thing anyway, because there's no explanation of how income inequality is supposed to make people obese. Toynbee seems to think it's (roughly) something to do with self-esteem, but doesn't really offer any evidence for this. I doubt that anyone's likely to get to the bottom of this one just using summary statistics.
(As an aside, you might be wondering what the Gini coefficient is or why it's a useful measure of income inequality. Wikipedia will tell you that it's defined as the area between the Lorenz curve of a distribution and the Lorenz curve of a uniform distribution, which sounds easy to calculate but not obviously meaningful; and MathWorld will tell you that it's the normalised mean of the absolute difference between each pair of incomes in the distribution, which sounds much more sensible but a pain to compute. These two definitions appear to be completely different, but surprisingly enough they turn out to be the same. Isn't that nice?)
More feedback on my piece on European election candidates, this time on behalf of Jim Naisbitt, about whom I was able to find out no information. Mr. Naisbitt now has a web site setting out his policies; thanks to Linda Holder (who I'm guessing designed the site?) for drawing it to my attention.
Mr. Naisbitt is a 65-year-old civil engineer originally from Gateshead. (Among other things it appears that he spent part of the early '70s designing bits of Iraq's water supply system; probably the Americans have since bombed them, which is sad.) He, like me, appears to be fairly disillusioned with the governance of the European Union, and he's also noticed that the electoral system itself is bloody stupid:
Furthermore, I have put up a Deposit of £5,000 [to stand in the election] and, to save this, I must win 2.5% of the vote. A Party List of SEVEN Candidates needs also to win only 2.5% (not 17.5%) and also puts up a total of only £5,000 (NOT £35,000 as one might expect!). The tradition of the Individual in British Society is being trampled by the Herd.
As for policies, well, he has a bulletin which isn't very specific, but mentions that he is in agreement with the Westminster Declaration of the Movement for Christian Democracy. That site seems to be down right now, but you can read the text of the Declaration at web.archive.org. It seems -- as I had suspected -- that Jim's statment that, ``The Declaration is concerned with the Sanctity of Life'' is code for ``I oppose abortion''.
However -- and here I again return to the very edge of eye-popping rage -- imagine that I felt that Mr. Naisbitt, like Martin Bell, were worthy of my vote. Because of the fucking idiotic electoral system, I would have to choose only one of them -- whereas were they part of a party, even one they'd made up for the purpose, for instance the `This Electoral System Is Bloody Stupid Party', I could vote for both. In any case I've been disenfranchised. The only reasons that this hasn't provoked full-blown eye-popping rage are that (a) this election doesn't really matter anyway; and (b) I've had my morning coffee and am therefore feeling less cranky than I otherwise might.
(I will also point out that the behaviour of Ms. Holder, who sent me a polite and informative email entirely bereft of threats of litigation, should serve as a lesson to Steven Uncles of the English Democrats in how civilised people hold discourse on the web. Not that that'd be of interest to him, I suppose. In the unlikely event that anyone is planning to vote for the English Democrats, I'd strongly advise them to vote for Mr. Naisbitt -- or anyone else, apart from the BNP, Respect Coalition or UKIP -- instead.)
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