That is the big question everyone is asking.

You, I, even your crazy Uncle Jim who never “got over ‘Nam” don’t shoot-up elementary schools or their company headquarters. That leaves us to wonder what makes mass public shooters different that the rest? What causes them to disconnect from reality and society to the point where mass murder seems like a good idea to them?

Well, we now may have some numbers to (partially) answer the question.

The Major Takeaways about Mass Public Shooters

• Mental illness is confirmed (yet again) as a significant contributor.
• We now have some hard numbers showing that addiction to violent videos games may be contributory.
• Social media looks like it drives people crazy (but most of us know enough to put down our devices from time to time).
• Being a bully, having some childhood trauma (which may have turned someone into a bully), and being on the autism spectrum (as we showed before) can be contributory.
• Mass public shootings (MPS) are becoming increasingly planned events and so too is incorporating “cattle pen” scenario selection.
• Lack of containment of, and/or amplification of negative/antisocial emotions appear to be the net driver.

The Violence Project

Some criminologists launched The Violence Project with the mission of digging into the underlying causes of mass murder. They were kick-started by a grant from the National Institute of Justice, a government agency that is focused primarily on criminology and related topics. In other words, they are pros who know the business (unlike, for example, a pediatric surgeon working for the Bloomberg School of Public Health at John Hopkins).

Things that make their database insanely useful include:

• It goes back much further than most MPS databases.
• They have unprecedented access to non-public information (including mental health records of shooters).
• They incorporate a huge number of variables… sneaking up on 200.

Onto their database, we added a couple of columns of data from the Gun Facts MPS database that are unique to the Gun Facts project.

Our goal was to see, statistically, what underlying variables are most tightly associated with someone going bonkers and killing people by the dozens. As always, the answers are surprising.

The Method is not Madness

WARNING! If discussion of statistics and research methodologies make your head hurt, then skip ahead to the next section. This section is for the nerds.

We followed a very common approach to isolating the most likely causes that could catapult a person from being an acceptable citizen to a mass murderer with a preference for MPSs:

1. Performed a regression for each variable (we skipped past variables that previous research showed to be poor predicators for MPSs, and some that simply were not interesting to us, such as the period of time a personal crisis occurred before the MPS).
2. Eliminated variables with a low score (using the R² regression test).
3. Performed a multivariate regression on the remaining variables, testing against both the number of MPSs in each year and the number of people killed in MPSs (at some later date we’ll repeat this step for the average number of people killed per incident per year).

What We Discovered

Welcome back, those of you who skipped statistics class too often in school.

Whittling down, we found eight variables that made it onto the short list of possible contributing factors and five that were statistically probable contributing factors.

What caught our attention is that some variables are much more predictive of the number of people who will be killed in an MPS than the overall number of such events in a given year. In other words, some things make people want to go on a rampage and other things make them want to get a new high score on the Mass Shooter Scoreboard.

A mass shooter often commits domestic abuse, and those who kill many strangers in an MPS are also likely abusers. This makes a bit of sense – if you are the type who, in a fit of uncontrolled rage, would beat your wife, kids or elderly parents, then murdering a bunch of people when life throws you a curveball is not unthinkable.

Likewise, people who are obsessively consumed by social media tend to get (pardon the pun) triggered. Social media, especially on Twitter, is a source of constant aggravation. People who do not handle aggravation and bitter arguments (online or off) may not be able to channel their cumulative rage effectively.

Violent video games are a contributing factor, though there is a note of caution here (and after reading this blog, grab a copy of Assassination Generation to read some of the psychology industry’s insights into this). In terms of the number of people killed in MPS, addiction to violent video games was moderately associated; but the problem is, violent video games have not been around all that long. Indeed, the Violence Project database does not track this to before 1992, and we have to understand that the number and graphic excess of these games increases every year. All that noted, the association was weaker in terms of the number of MPSs in any year. We can say that violent video games may moderately increase the number of incidents (though the statistical test is weak, p-value not below 0.05) but may well cause some shooters to become competition killers and attempt to set the new high score.

On the mental health front, we have a field of landmines to contend with. You can see that having been previously counseled by a psychologist or psychiatrist shows a moderate association with a high body count on an annual basis. But it does not affect the likelihood of committing an MPS itself. In other words, if someone had a significant enough mental health issue to have received counseling, they are not much more likely than the population at large to shoot-up a movie theater, but they are more likely to plan out an attack and take a lot of lives if they do.

Crazy + Planning = Body Count.

Where this gets a bit odd is that the Violence Project tracks a bunch of psych symptoms, reported from news media, that are not at all associated with either the number of MPS or the number killed in any given year. This is likely a limitation of news reporting. In the absence of a psych evaluation, the odds of (a) someone who knew the shooter (b) offering an insight to an (c) unbiased journalist is very low. Hence, we did not see a statistical association with shooters and recent/ongoing stressors, depressed mood, being unusually calm or happy, rapid mood swings, increased agitation, abusive behavior, isolation, losing touch with reality, paranoia or even suicidality.

What to make of this mess

I had a very tightly wound girlfriend once who noted that she would behave badly until someone put her in her place (“Knock it off, Sally” would do the trick, I discovered). But I also witnessed her bad moods escalated under certain stressors (buy me a cup of coffee and I’ll tell you the story of a particularly weird New Year’s Eve).

Containment and amplification… a deadly combo?

A domestic abuser lacks outside “containment.” Too rarely does an elder male family member come around and drag the abuser into the street for a not-so-subtle attitude adjustment. Likewise, not limiting the amount of time one exposes themselves to things that amplify bad feelings (social media, TV news, violent video games, the Kardashians), along with intent, appear to drive MPS.

Take for example this passage from the manifesto left behind by the Isla Vista rampage shooter. “This was the point when my social life ended completely. I would never have a satisfying social life ever again. It was the beginning of a very lonely period of my life, in which my only social interactions would be online through video games.” This is a double whammy. Addiction to violent video games removes the containment that social interaction affords (e.g., the need to behave in socially acceptable ways) while also amplifying violent urges and antisocial responses.

As we look into the data and into the world around us, watch for people who lack containment of bad impulses and who may be spinning into a maelstrom of antisocial amplifiers. This may be the center of the storm for mass public shooters.