At a midnight showing of the Dark Knight early Friday morning, a single attacker walked into a movie theater in Denver dressed in body armor and heavily armed with two guns and a knife. He threw two smoke bombs into the theater and then opened fire on random audience members. The indiscriminate nature of the attack is appalling, but it dramatizes the post-columbine era of violence. Disturbed people are willing to kill unknown others, and the phenomenon isn’t limited to just the historically violent United States.
On Wednesday, an indiscriminate shooting in Toronto left two young people dead and more than 20 others wounded. The attack took place at a block party in a housing complex, in plain view, exhibiting the felt trend toward reckless public shootings.
Does the Toronto shooting cast doubt on the ability for gun control laws (which are stricter in Canada) to reduce such random violence? The question is hard to answer statistically, but there are some things to note when comparing, for example, the U.S. and Canada.
For starters, it’s worth noting that there is a strong correlation at a high level of statistical significance between the rate of gun ownership in a country and the homicide and suicide rates of the country. This means that as more households own guns in a country, there are more killings with guns as a percentage of the population.
This is useful to know, but can be a little deceptive. A country might have a high gun homicide rate simply because its homicide rate is high overall. If there is just a lot of violence in a country, then it would not be surprising that lots of people would own guns and that they would be used a lot. In such a case, gun ownership would not be driving a high gun homicide rate but just be a consequence of a violent society in general.
However, there is also a very strong correlation between total per capita homicides (from all sources) and gun ownership. If you add this relationship to the one above, the whole picture becomes more suggestive: societies with less guns have less overall killings and a smaller percentage of those killings are committed with guns.
And if, as gun rights advocates point out, criminals can get guns when they want, but don’t commit any more crimes than they would otherwise commit when guns are around (they just use them as a tool for a crime they already intend), then why would the percentage of homicides committed with guns go down when fewer people own guns? The proportion should stay the same as criminals use guns in the same circumstances.
This suggestive pattern is exactly what one sees when comparing Canada and the U.S. side by side. There are less guns in Canada, there are less overall gun homicides, and the gun homicides that do take place make up less of a percentage of the total per capita homicide rate.
These results are not decisive (as I said, only suggestive). Perhaps criminals in the U.S. just delight in using guns and if we had more controlling gun laws, the same people would commit more crimes because ordinary citizens were less able to protect themselves.
Evaluating the deterrence effect is so difficult because there is not a practical, ethical way to run an experiment in which guns are randomly assigned to people in various areas so that the effect of those guns on the homicide rate could be evaluated next to what happened in places where guns were not given out. You can’t just force people to have guns because for guns to be a deterrent, the owner has to want the gun and take time to learn to use it. And if the person is doing all that, they are probably reacting to something in the environment. Gun ownership would thus be a dependent variable and not an independent variable.