Firearm prohibitionists love to use tragedy to leverage their agenda. So, it’s important for gun rights advocates to stand their ground and fire back (proverbially) whenever this happens.

I posted a graphic on Facebook claiming the average number of people killed in mass shootings when stopped by police is 18.25, and the average number of people killed in a mass shooting when stopped by civilians is 2.2. I based it on 10 shootings I found listed on some timeline somewhere. I honestly don’t even remember where. I presented the case studies in a blog post on the Silver Circle blog and I did the math myself.

The graphic was met with great enthusiasm and much skepticism. Leave it to Facebook users to demand an audit on a meme. So, I started over, only much more meticulous this time. I compiled and analyzed 100 shootings, noting my methodology, and I am now prepared to present my findings, complete with links to the data. But here’s a spoiler… It’s not that different.

The average number of people killed in mass shootings when stopped by police is 14.29

The average number of people killed in a mass shooting when stopped by a civilian is 2.33

I was so close! Here’s what I think accounts for the difference. In the first sample there was likely a selection error based on what grabs headlines. Larger shootings get more press, so if you take a small sampling you’re going to be working with a data set of the worst shootings. As for the consistency of the civilian statistic, it makes perfect sense if you think about from inside the mind of a heroic civilian with a concealed carry permit. It goes something like this:

BANG!

“Holy crap! that guy shot that other guy.”

BANG!

“He’s just going to keep shooting people.”

BANG!

And the shooter goes down.

Quite a few cases went something like that. In fact, I found only one example of a shooter stopped by civilians who killed more than three people. Jared Loughner killed 6 people in Tucson, Arizona before he was tackled by two civilians. An astute reader informed me that at least one of the civilians that helped stop Jared Loughner was carrying a concealed weapon, but he did not use his gun out of concern for innocent bystanders.

I want to be perfectly clear. I am not much of a firearms enthusiast. I don’t own a firearm. I’ve only ever been shooting twice. For me it’s not an issue of gun rights. It’s about property rights. A person has a natural right to own a hunk of iron in any damn shape they want, and they shouldn’t be criminalized until they use that hunk of iron to harm someone. People can argue crime statistics ’till they’re blue in face. I frankly don’t care about people’s ideas for managing society.

What I am is a math enthusiast. So, without further delay, here’s how I arrived at these numbers.

Step One: Amassing a data set

I searched for timelines of shootings and selected 5 that appeared the most comprehensive.

While doing this I learned some important vocabulary. A “spree shooting” is when a killer murders in multiple locations with no break between murders. As in the Virginia Tech killer who began shooting in one hall, and then walked across campus and continued shooting in another hall. A “mass shooting” is when a killer murders multiple people, usually in a single location. As in the Fort Hood shooter who killed 13 people at one military base. A “school shooting” can be either of these as long as one or more locations is a school. As in the Columbine shooting, which is also classified as a spree shooting because they went from room to room. The term “rampage shooting” is used to describe all of these, and does not differentiate between them. So that is the term I’ll be using from here on out.

As many have pointed out, none of the weapons involved are “automatic weaponry” or “assault rifles” but they are often misreported as such by media outlets that lack knowledge of firearms.

I selected these lists because they were the most comprehensive of those that I found, and I was seeking as large a data set as possible. I combined them all, including the first 10 from my previous post, and removed all redundant data for a total list of 100 shootings.

Step Two: Trimming irrelevant data.

While the list was comprehensive, the details about each shooting were not. In each shooting I had a date and a location, but often important details, like the number of people killed, or how the shooter was apprehended were missing. So, I set to the long task researching each incident to fill in the missing data. I didn’t incorporate the number of wounded people because so many were not reported. But the reason they call a single death a shooting rampage is because there were many injuries. All relevant data is contained in the links in the finished list below or in the timelines linked above. Most of the data came from either Wikipedia, a mainstream news article about the incident, or a handy resource I discovered called Murderpedia.

Next I removed incidents that did not fit within the scope of this analysis. Even though every incident on the list was a shooting, not every incident was a rampage shooting. So, I selected for incidents that included at least some indiscriminate targeting of bystanders. I removed incidents like Dedric Darnell Owens who shot and killed his classmate Kayla Rolland and then threw his handgun in a wastebasket (*meaning I removed incidents where the shooter killed all he was going to kill and stopped, because neither police or civilians actually reduced the deaths at the scene.) And I removed incidents like Michele Kristen Anderson who killed her entire family at a Christmas Party. So what remained were specifically rampage shootings in which a killer went someplace public and began firing at random people.

Suicide presented a tricky variable in the analysis. Roughly half of the remaining rampage shooters ended their own lives. So, I removed all incidents where the shooter killed themselves before police arrived reasoning that they had killed all they were going to kill and police had no impact in stopping them. Theoretically these incidents could have been stopped sooner by a civilian, but let’s not speculate. What I left in were incidents where shooters commit suicide after engaging the police, either during a shootout with police, or after a chase. I included, for example, Jiverly Wong, who witnesses say stopped shooting and killed himself as soon as he heard sirens but before police arrived, crediting the police’s response time with stopping the murders. But I did not include the shooters themselves in the total number of people killed.

I also removed cases like Edward Charles Allaway who shot up a library, then fled to a nearby hotel and called police to turn himself in, and cases like Darrell Ingram who shot up a high school dance and fled the scene only to be apprehended later after a long investigation. I was only looking for incidents when intervention from police or civilian saved lives.

What remained was 32 cases of gunmen firing indiscriminately whose rampage was cut short through the intervention of either a civilian or a police officer.

Step Three: The List

I divided the remaining cases into two categories, those stopped by police and those stopped by civilians. I included both armed and unarmed civilians for reasons that will become clear in the final analysis. I also removed cases like Dominick Maldonado and Charles Joseph Whitman. Moldonado went on a shooting rampage in a shopping mall in Tacoma, Washington, and ultimately surrendered to police but was confronted by two legally armed civilians who interrupted his shooting. They did not fire for fear of hitting innocent bystanders. Whitman climbed a tower at the University of Texas in Austin, Texas and began shooting at other students and faculty with a sniper rifle. The police who stopped Charles Whitman were assisted by a civilian with a more powerful rifle. I’m calling incidents like this an assist from civilians and removing them from the analysis as anomalies.

Step Four: Final analysis

With 15 incidents stopped by police with a total of 217 dead that’s an average of about 14.29. With 17 incidents stopped by civilians and 45 dead that’s an average of 2.33.

The first point I want to draw your attention to is that roughly half of shooting rampages end in suicide anyway. What that means is that police are not ever in a position to stop most of them. Only the civilians present at the time of the shooting have any opportunity to stop those shooters. That’s probably more important than the statistic itself. In a shooting rampage, counting on the police to intervene at all is a coin flip at best.

Second, within the civilian category 11 of the 17 shootings were stopped by unarmed civilians. What’s amazing about that is that whether armed or not, when a civilian plays hero it seems to save a lot of lives. The courthouse shooting in Tyler, Texas was the only incident where the heroic civilian was killed. In that incident the hero was armed with a handgun and the villain was armed with a rifle and body armor. If you compare the average of people killed in shootings stopped by armed civilians and unarmed civilians you get 1.8 and 2.6 but that’s not nearly as significant as the difference between a proactive civilian, and a cowering civilian who waits for police.

So, given that far fewer people die in rampage shootings stopped by a proactive civilian, only civilians have any opportunity to stop rampage shootings in roughly half of incidents, and armed civilians do better on average than unarmed civilians, wouldn’t you want those heroic individuals who risk their lives to save others to have every tool available at their disposal?

* Updated 12/15/2012 – This article was originally posted shortly after the Dark Knight premier shooting in Aurora, Colorado, but I have continued to refine the data set and update the statistics. I am especially grateful to all the knowledgeable commenters who have helped correct my errors. I was also contacted by a college professor who I supplied with all my research notes, so they can be peer-reviewed and perhaps published in a more academic setting. So, in light of the recent tragedy in Newtown, Connecticut that has left 27 dead, including 20 children, I updated this article to reflect shootings that have occurred since the Aurora, Colorado shooting, and corrected the errors that readers brought to my attention. I have preserved the integrity of the original analysis and have only updated the raw numbers and a few factual errors.

Tags: Columbine, firearms, Fort Hood, James Holmes, Jared Lee Loughner, shooting rampage, Virginia Tech