Guns per Capita and Homicides – Is There a Correlation?

Here’s a statistics quicky. A while ago, just after the tragic shooting at Sandy Hook Elementary School, I wanted to produce a clear proof that gun ownership and homicide rates are correlated. It seemed logical to me that, plus / minus statistical fluctuations, the phrase “more guns, more violence” holds true. So I extracted the relevant data for all first world countries from Wikipedia and did the plot. Here’s the picture I got:


Maybe you are as surprised as I was. Obviously, there’s no relationship between the two variables, more guns does not mean more violence and less guns does not mean less violence. So whatever the main cause for the violence problem in the US (see the isolated dot in the top right? That’s the US), it can’t be guns. And that’s a liberal European speaking …

Just in case anyone cares, I blame the gang and hip-hop culture. I can’t be guns (see above), but it also can’t be media or mental health or drugs (people in all other first world countries also play shooter games,  watch violent movies, have mental problems, buy and sell drugs).




The Probability of Becoming a Homicide Victim

 Each year in the US there are about 5 homicides per 100000 people, so the probability of falling victim to a homicide in a given year is 0.00005 or 1 in 20000. What are the chances of falling victim to a homicide over a lifespan of 70 years?

 Let’s approach this the other way around. The chance of not becoming a homicide victim during one year is p = 0.99995. Using the multiplication rule we can calculate the probability of this event occurring 70 times in a row:

 p = 0.99995 · … · 0.99995 = 0.9999570

 Thus the odds of not becoming a homicide victim over the course of 70 years are 0.9965. This of course also means that there’s a 1 – 0.9965 = 0.0035, or 1 in 285, chance of falling victim to a homicide during a life span. In other words: two victims in every jumbo jet full of people. How does this compare to other countries?

 In Germany, the homicide rate is about 0.8 per 100000 people. Doing the same calculation gives us a 1 in 1800 chance of becoming a murder victim, so statistically speaking there’s one victim per small city. At the other end of the scale is Honduras with 92 homicides per 100000 people, which translates into a saddening 1 in 16 chance of becoming a homicide victim over the course of a life and is basically one victim in every family.

 It can get even worse if you live in a particularly crime ridden part of a country. The homicide rate for the city San Pedro Sula in Honduras is about 160 per 100000 people. If this remained constant over time and you never left the city, you’d have a 1 in 9 chance of having your life cut short in a homicide.

Liked the excerpt? Get the book “Statistical Snacks” by Metin Bektas here: http://www.amazon.com/Statistical-Snacks-ebook/dp/B00DWJZ9Z2. For more excerpts check out Missile Accuracy (CEP), Immigrants and Crime and Monkeys on Typewriters.