Saturday, August 25, 2012

Dan on crime - a lesson in the abuse of statistics

Dan O'Brien, writing in the Irish Times on Friday, claims that poverty and inequality are "not key reasons for law breaking" and that "recessions have had no discernible effect [on crime rates]". I call bullshit, and here's why (written as a direct reply to Dan's article, this is an edited version of the comment I left on the Irish Times site).


"Aw, people can come up with statistics to prove anything Kent. Forty percent of all people know that."
            - Homer J. Simpson


Wow, this is a breathtakingly ill-informed piece of lazy journalism, and an outrageous abuse of statistics!

The commenters on the site have already pointed out some of the flaws in your argument, but there are other ways in which this is simply wrong.

For anyone interested in a serious discussion of incarceration, I would highly recommend David Cole's article from the New York Review of Books from a few years back (and which I previously blogged about here).

According to Cole, “most of those imprisoned are poor and uneducated, disproportionately drawn from the margins of society” (referring to the US prison population).

The US has by far the highest incarceration rate in the world. However, somewhat inconveniently for your argument, Cole also points out that up to 1975 the US incarceration rate had been steady at about 100 per 100,000. Since then, the rate has ballooned to 700 per 100,000. If putting the crooks behind bars is really what prevents crime, it seems strange that such a massive increase in the incarceration rate apparently had no preventative effect on the 'crime waves' of the 1980s, to which you also make reference.

Incidentally, it is also slightly inconvenient for your argument that Russia, a country that you refer to as having “a very high murder rate”, also has the second highest incarceration rate in world. Huh.

But of course all of these superficial correlations are meaningless anyway (as you point out yourself!). What you are doing is taking two trends that happen to be moving in the same direction (or in some cases opposite directions), and assigning causation, in blatant disregard of your own caveat about correlation not necessarily implying causation!

Your country comparisons are also spurious. You simply can't compare crime rates and income levels across countries without at least attempting to control for some other relevant factors. Any applied economist worth their salt would know this. Two such relevant factors, which you mention in your article, are the rate of drug use (or perhaps more importantly narcotics production) and demographics. Controlling for these might lead to a very different picture of the relationship between income and crime (or it may not, the point is we simply don't know, based on the evidence you present). In any case, it seems likely that relative poverty and relative deprivation (i.e. within countries) would be more important drivers of crime than aggregate national income levels.

It is astonishing that you would make such sweeping assertions about what does or does not cause crime on the basis of so little evidence, and that the Irish Times would publish this piece seemingly without having done even the most basic fact-checking. (On that point, it is worth referring to Paul Krugman's recent article in which he outlines the fact-checking process that each of his op-ed pieces goes through before being published in the New York Times.)

You have done a disservice to economics and statistics with this article – as well as showing an almost total disregard for the other social-sciences which have produced voluminous literatures on the socio-economic causes of crime. I sincerely hope that the Irish Times will give the opportunity to someone with some expertise in this area to write a response to this article.

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