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"The whole country... knows the problem was there weren't enough good guys with guns," NRA honcho Wayne LaPierre said in the aftermath of the Navy Yard shooting in Washington, D.C. It's a a favorite trope of the gun advocate. Since the NRA receives plenty of backing from gun manufacturers, we usually assume that LaPierre means people ought to buy more guns. But if you remember how hard it is for the NRA to fill its membership rolls, it makes you wonder if he's referring to the other side of the equation. After all, with nearly one gun for every man, woman, and child in America — almost double the per capita number of guns in the next highest nation, Serbia — there are plenty of guns out there. But do we have enough good guys?

How many good guys are there in America?

The first question we needed to answer was: What's a good guy? The easy and correct answer is: Any American who is carrying a gun. So we know precisely how many good guys there could be in America; as of the 2010 Census, about 308 million. Here's how they break down by state, at right. Done.

Oh. Except that technically people who aren't yet 18 aren't allowed to carry handguns around, by federal law. So we need to take them out of the mix, giving us the map at right, and a grand total of about 234 million in 2010.

Well, this isn't entirely accurate either. After all, an American with a gun is a good guy up until such time as he starts killing other Americans. Mark David Chapman was just walking around New York City being a good guy, and then he became a bad guy, unfortunately. Americans are allowed to murder other Americans if their targets are themselves about to murder or appear to be about to murder innocent Americans. This is known as the Zimmerman Contingency.

So we decided to take out known bad guys; that is, those Americans who have been convicted of a crime and served time in a federal or state institution. By federal law, they aren't allowed to purchase firearms, though the NRA contests that. (Born-again good guys, if you will.) Finding data on how many people in each state fit that criteria is hard. We reached out to the government's Bureau of Justice Statistics, but they don't collect the data.

Instead we turned to the Sentencing Project, which last year compiled data on those voters in each state that were disenfranchised due to criminal history. These are known bad guys, so we pulled them out of the mix. Leaving us with about 228 million possible good guys (though that group still includes a lot of felons).

How many good guys do we need?

But is that enough? Would 228 million armed Americans be enough to prevent mass killings and home invasions and probably all other crime? (Bearing in mind that each year, some of those good guys would become bad guys by virtue of killing Americans who weren't themselves in the process of killing bad guys.)

To figure that out, we had to figure out how many good guys with guns we needed in order to drop the crime rate down to zero. Happily, the FBI last week released its 2012 "Crime in the United States report. This annual document breaks down crime data from municipalities and states across the country. It also counts the number of officially sanctioned good guys in each place, which is to say the number of cops. Which allows us to do something interesting. Below, a graph contrasting the rate of violent crime for every 1,000 residents of every municipality in America with a population of more than 1,000 people with the number of sworn police per 1,000 people.

Kind of cluttered, so we added a trend line, allowing us to see how the correlation works. If Wayne LaPierre is right, which he always is, we'd expect a line from the upper left to lower right, suggesting that fewer good guys means more violent crime, and that there's less violent crime in places with more cops. And:

Not exactly that. There is a correlation between having more cops and having more violent crime, in fact — which you might expect if cities were responding to more frequent crimes by hiring more police. But this certainly suggests that the good-guys-with-guns theory has some problems in practice.

Except maybe that data turns around if we start seeing more of our 228 million potential good guys stepping up to the plate. Well, we can look at that, too. A recent study calculated the rate of gun ownership per state as of 2010. (It also found that each percentage point increase of that figure increased the rate of gun-related homicide by 1 percentage point, somewhat undermining LaPierre yet again.) We took the data from that study and compared it to 2012 violent crime data for each state. Giving us this graph, with the red line again showing the trend.

And again we see that a correlation between more guns in the hands of noble American good guys and more violent crime.

So how many good guys with guns do we need to eliminate violent crime? Apparently fewer than we already have. Fewer citizens with guns, the data suggests, less violent crime. Which if you think about it, sort of makes sense.

Top image via Marxchivist's Flickr.

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