The number of guns per capita per country was a strong and independent predictor of firearm-related death in a given country, whereas the predictive power of the mental illness burden was of borderline significance in a multivariable model. Regardless of exact cause and effect, however, the current study debunks the widely quoted hypothesis that guns make a nation safer.
There is little question that the combination of mental illness and easy access to guns may prove to be synergistic in their lethality, as was seen in the shootings in Aurora, Tucson, at Virginia Tech, in Oak Creek, and other places in recent years. On the opposite end stands the contention that fewer firearms would reduce crime rates and overall lead to greater safety. Yet many of these arguments from both sides are based on little or no evidence. We sought to evaluate the relationship between prevalence of gun ownership and mental illness on firearm-related death in a given country.
Looking at international data, here's what they found:
In having almost as many guns as it has people, prevalence of private gun ownership was the highest in the US among both developed and developing countries. Japan, on the other end, had an extremely low gun ownership rate (see Table below). Similarly, South Africa (9.4 per 100,000) and the US (10.2 per 100,000) had extremely high firearm-related deaths, whereas the United Kingdom (0.25 per 100,000) had an extremely low rate of firearm-related deaths. There was a significant positive correlation between guns per capita per country and the rate of firearm-related deaths ( r ¼ 0.80; P < .0001) ( Figure, A ), with Japan being on one end of the spectrum and the US being on the other. In this correlation, South Africa was the only outlier in that the observed firearms-related death rate was several times higher than expected from gun ownership.

http://www.commondreams.org/headline/2013/09/18-1