In the wake of a terrible tragedy, talks about gun control are at the forefront of today's political stage. Of course, both advocates and opponents of gun control point to the Connecticut shooting as a validation of their own viewpoint. It's unfortunate that occurrences like this only seem to polarize us further. We can't rely on anecdotes or emotion to solve this problem. So, what does the data say?
Using data from the Guardian on gun ownership by country, I evaluated the hypothesis that higher rates of gun ownership either (A) lead to increased gun violence (as believed by the left) or (B) actually work to deter gun violence (as believed by the right.) Note that without an experimental manipulation (which is difficult to do due to the many factors that would need to be controlled for, not to mention very questionable ethics), we can identify correlations but it's difficult to really say anything about causation.
First, I compared the total number of civilian-owned guns in each country to the total number of gun-related homicides. The results, unsurprisingly, show a strong positive correlation, most of which can be explained by population: more populous nations will tend to have more homicides and more guns. (In these figures, the size of each data point indicates population.)
To control for population, I compared the rate of gun ownership (per 100 people) to the rate of gun-related homicides (per 100,000 people) and the results were surprising. There's a weak positive relationship between the rate of firearm ownership and the rate of firearm-related homicide (p=0.25), which doesn't strongly support either side's claims:
I suspect that there are other cultural, political, and socioeconomic factors that far outweigh gun ownership as predictors of gun violence, and that both sides in this debate potentially have valid points. In some situations, the presence of guns may deter violent crime. In others, it may enable violent crime.
We can all agree on one thing: we want there to be less mass shootings in America. When considering what policy changes will move us toward that goal, it is absolutely essential that we rely on evidence instead of either emotions or anecdotes.
Additionally, since "guns don't kill people (people with guns kill people)", maybe gun control is less important to curing the modern epidemic of mass-shootings than improving access to and understanding of mental healthcare.
The data and code I used to produce these figures is available on GitHub, and you're free to use them however you like. Feedback is welcome.
Edit: Someone did some additional analysis, uncovering a couple interesting correlates of overall homicide rates (including those unrelated to guns): GDP and income inequality. See it on Reddit.