2 June 2009

All too often, I find myself reading about how gun control legislation is important to protect the lives of citizens, all "proven" by gun crime statistics in the US. In one discussion in particular, a individual stated a fact that guns account for the weapon of choice in more murders than all other weapons combined which means they're too dangerous to allow people to have. This says nothing at all about the actual murder rate, and the effect of gun control legislation on the murder rate — just that, even if the murder rate is lower in the presence of firearms, guns end up having the largest share of the murder market in the US.

An alternative theory of the statistic might go something like this:

  1. More guns in the hands of private citizens discourage people from committing murder with knives.

  2. The number of murders with knives declined, and the number of murders with guns remained constant.

  3. The overall number of murders decreased because of the decline in knife murder rates, so the percentage of murders committed with guns increased even though the number of gun murders remained constant.

I don't have any idea whether that's an accurate explanation for the higher rate of gun murders than knife murders in the US. The statistical basis for proving or disproving this kind of theory of the effect guns have on murder rates doesn't exactly exist. It certainly is a plausible-sounding hypothesis, though, and no less supported by the lone statistic of 68% of murders in the US in 2006 being committed with guns.

The same guy, in the same comment where he pointed out that more murders are committed with guns than with any other weapon in the US, also linked to UK gun crime figures. Well, sure, let's compare crime rates in the UK with those in the US. We've already established that gun crimes are more numerous in the US than knife crimes, and I'll stipulate for the sake of argument that gun crimes are more numerous in the US than in the UK (though there are niggling holes in that comparison, too). Let's try a different comparison. Note that I'm probably overestimating the UK population and underestimating the US population in these statistical comparisons, which favors the UK in terms of estimating low crime rates (since these rates are measured per capita). The same goes for the fact I'm underestimating UK crime incidences and overestimating US incidences. Despite heavily favoring the UK for determining the per capita statistics, I think you'll find the results illuminating:

Statistical studies can be great tools for determining the results of policy changes, but the devil lies in the details. Simply picking a number out of thin air — like the fact that 68% of murders are committed by the use of a firearm in the US — in no way proves anything other than that 68% of murders are committed by the use of a firearm. That alone doesn't mean you're in more danger in the US because of laxer gun control legislation than in the UK, where firearms are all but entirely prohibited (hey, at least the police can check them out of the supply room under very extreme circumstances — right?).

Note that even the statistical comparisons I present here are not sufficient to prove a case. There are too many other variables in comparisons between crime rates in the UK and in the US to reasonably expect any real certainty about exactly what effect gun control laws have in either country. A far more reliable statistical comparison for purposes of determining the effect of gun control legislation is, as I pointed out in gun control arguments aren't exactly "rigorous", to compare crime statistics before the passage or repeal of a gun law to those after the passage of the law — say, the three years prior and the three years after. Other factors will come into play, but given enough case studies, trends will definitely be seen to emerge.

If you aren't prepared to produce statistics like that, you aren't prepared to produce statistics that prove anything worthwhile about the efficacy of gun control legislation.

statistical sources: