Guns are the Tools that People Use Most Often to Kill People

Intro. A good friend has a habit of re-posting on facebook annoying and silly claims about guns. No, I don't want to de-friend him. Mostly I ban the source of the claims but he finds new sources of material. When I attempt to verify some claims, the claims are easily refuted by a quick google search and the first link to Wikipedia.

The most specious of gun-related claims is the 'guns don't kill people, people kill people'. If you want to play it that way, fine. Cars don't drive people, people drive people! Scissors don't cut paper, people cut paper! Knives don't chop vegetables, people chop vegetables! A gun is a tool, as are cars, scissors and knives. I use my car most days to transport me around town, I use scissors perhaps weekly to open mail or cut sheets of paper to needed size; I use knives for daily preparation and consumption of food. Cars, scissors and knives are tools that occasionally get used to kill people. Still, soccer moms/dads and taxi drivers don't kill many folks intentionally with their cars, second graders use scissors for art projects without managing to kill anyone, and chefs and cooks and food-eaters of all kinds use knives without stopping someone's beating heart. 

Data. Being a statistician, what I did do is get data from Wikipedia on numbers of murders and population broken out by state. Wikipedia got its data from the FBI Uniform Crime Reporting Statistics. The FBI for 2010 seemed to be missing data from Florida, but Florida publishes the data for us, and the Florida and FBI sources match the data in the Wikipedia article. That particular Wikipedia article also gave 2010 state population. I subtracted gun murders from total murders to give non-gun murders by state and calculated gun and non-gun murder rates.

Results. The first figure plots numbers of murders (gun and non-gun separately) in a state against state population on a log-log plot with lowess curves (iter=0) for both murder types. Gun murder counts are generally greater than murder counts using all other tools combined. For most of the state population range, the lowess curves are linear and parallel, suggesting that the number of murders of either type goes up as a power of the population. Fitting a simple GLM suggests the power is about 1.1 for both gun and non-gun murders, only slightly larger than 1. 

Only for the smallest population states do the two lowess curves intersect. Checking the data, eight, mostly northerly, mostly smaller states have non-gun murder counts higher than their gun-murder counts; these are Hawaii, Maine, New Hampshire, North Dakota, Oregon, Utah, Vermont and West Virginia. The total number of murders with all tools in those 8 states was 262 with 34 more non-gun murders than gun murders.  In contrast, there were 13540 murders in the other 42 states. 

We can also look at gun and non-gun murder rates by state as well; these are given in the second figure. Non-gun murder rates barely increase with population size, while gun murder rates do increase with population size, until somewhere just after 5 million people when the rate of growth tapers off. 

Conclusion. For 2010 there were 9,304 gun murders, and 4,498 non-gun murders in the 50 United States. In the United States in 2010, the gun is the primary tool people use for killing people. People use guns to kill people more than twice as often as they use all other tools combined. People use guns to kill people. 




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