Category Archives: mass killings

Deadly Events Are Contagious: Mass killings can trigger others

Roughly a quarter of mass killings and school shootings occur because of contagion — with one event increasing the chances of another happening — even if the suspect doesn’t consciously realize it, according a study released today.

Researchers at Arizona State University and Northeastern Illinois University used USA TODAY’s mass killings data, which tracks killings of four or more people since 2006. USA TODAY’s data, unlike other sets, include many events that do not receive extensive media coverage.

Monte Talmadge walks past a sidewalk memorial in front of the Emanuel AME Church after a mass shooting there killed nine people in June.
Monte Talmadge walks past a sidewalk memorial in front of the Emanuel AME Church after a mass shooting there killed nine people in June.

The researchers also used 15 years’ of data on school shootings, plus data about public shootings where at least three people were shot but not necessarily killed, from the Brady Campaign to Prevent Gun Violence. They fit all three data sets into a contagion model to see if one event had a ripple effect.

They found that the biggest events – mass killings and school shootings, which tended to get more publicity – had an average window of 13 days of contagion.

“What we think might be happening is the very small cross section of the public that’s vulnerable, that message gets to them and causes unconscious ideation to perhaps do something similar,” says Sherry Towers, professor of statistics at Arizona State University’s Simon A. Levin Mathematical, Computational and Modeling Sciences Center.

In the case of the recent Charleston, S.C. church shooting, there haven’t been any mass killings in the two weeks since. But there have been a rash of church arsons, which investigators are probing.

“Even though there doesn’t seem to be a contagion in this certain case, there does seem to be related events that have occurred,” Tower says.

Mass shootings with fewer than four deaths created no such contagion effect, Towers said. The researchers only looked at similar events, so they did not measure whether a mass killing or school shooting lead to an increase in single shootings, for instance.

Towers said she started wondering if school shootings triggered similar events in January 2014, after she was visiting the Purdue University campus when a student entered a campus building and shot and killed another student.

“There had just been three other school shootings in the news in the past week,” she said. “I just thought, ‘Is there something that’s causing these things to bunch together?’”

Other researchers have linked increases in suicides to high-profile suicides in similar contagion studies.

Towers says she hopes their findings will serve as a starting point for other researchers to look into the contagion effect further.

“This is a huge problem in the United States,” she says. “The chances of a person being killed in a mass killing is very low, but much higher in the US than in any other industrialized country.”

The study was published in the peer-reviewed PLOS ONE. USA TODAY’s mass killings data showed they happen every two weeks on average in the U.S. , and nearly a quarter do not involve guns. Explore USA TODAY’s map of mass killings in America

–Meghan Hoyer


That stomach-sinking feeling when data is wrong

That nagging feeling that something is wrong with the data? Listen to it.

When my colleague Marisol Bello asked whether we could figure out how often parents kill their children – she was reporting in the wake of a high-profile case in Georgia last summer – I knew we could probably find some help in the FBI’s supplemental homicide reports, which include victim/suspect relationship details. I ran the queries and came up with some preliminary figures, but I also knew the SHR was notoriously spotty, because many cities fail to provide details on murders.

So I started looking for other research on the topic, eventually digging up what can seem to be the gold standard of analysis: a piece co-authored by an Ivy League researcher, and published in a peer-reviewed journal. The only problem? The researchers had found six times as many filicides each year as I did in the FBI data.

I contacted the researchers. They hadn’t used the data directly from the FBI, but rather had used cleaned-up figures publically available from James Alan Fox and Marc Swatt of Northeastern University. That must account for the differences, they said.

But something kept bothering me: According to the researchers’ findings, 3,000 children each year were killed by their parents. Keep in mind that there are roughly 16,000 homicides each year. That would mean that 20% of all victims were children killed by a parent or stepparent. I covered the cops beat for the first four years of my career – I thought back to all the gang battles, lovers’ quarrels and drug deals gone wrong. I could count on one hand the number of child/parent murders I had seen. It certainly wasn’t anywhere near 20%.

So I followed the researchers’ lead, downloaded Fox and Swatt’s data and opened it in SPSS. It didn’t take long to realize each case number, which was supposed to be a unique ID, was in the file six times. A phone call to Fox, who walked me through the data, revealed the researchers’ mistake. Unlike the raw FBI file, Fox and Swatt’s dataset is built for advanced statistical analysis – it has multiple imputations to allow academic researchers to fill in holes that we know exist in FBI data, either where cases are missing entirely or where certain details (the relationship between victim and killer, for instance) aren’t included. Each killing was broken into six lines: the original record, and five different imputations with different weights applied and missing values filled in.

Fox walked me through a way to properly weight cases (his data set includes separate weights for national analysis and state-by-state analysis) and how to properly fill in gaps where relationship details weren’t provided in the raw data.

The upshot? I found that on average, about 450 children are killed by a parent or stepparent each year.

Brown University has since issued a correction to their press release on the researchers’ findings. Marisol and I used the data and our findings in a were published in USA TODAY, along with another follow-up story published later.

(a version of this post was published on the American Press Institute’s Fact-Checking Project blog)

–Meghan Hoyer

It’s not so easy to count mass killings

Two years ago this month, a particularly horrific mass killing took place in a Newtown, Conn., school. We’re still struggling with how we cover these crimes:

– In September, an FBI report on so-called “active shooter” cases was widely misreported to show that “mass shootings” were increasing. A federal definition shared by several agencies defines “active shooter” as “an individual actively engaged in killing or attempting to kill people in a confined and populated area.” For its report, the FBI make two tweaks: To include cases where more than one person was shooting and to drop “confined” to include outdoor events. It’s worth pointing out that many of these cases don’t meet the FBI’s definition of a mass killing: four or more dead, not including killer(s).

The FBI just wanted tactical insight, so it also excluded whole categories of potentially qualifying events: “Specifically, shootings that resulted from gang or drug violence—pervasive, long-tracked, criminal acts that could also affect the public — were not included in this study. In addition, other gun-related shootings were not included when those incidents appeared generally not to have put others in peril (e.g., the accidental discharge of a firearm in a school building or a person who chose to publicly commit suicide in a parking lot).”


Wrote the authors: “The study does not encompass all mass killings or shootings in public places and therefore is limited in its scope.”

Resulting headlines at major news organizations: “Mass Shootings on the Rise, FBI Says”;  “Mass Shootings on the Rise, New FBI Study Shows”; “FBI: Mass shooting incidents occurring more frequently”; “FBI study: Deaths in mass shootings increasing.” (Search users beware: A recent check finds many still uncorrected stories on the Web.)

– We continue to update USA TODAY’s interactive graphic of mass killings, published a year ago. We use the FBI’s definition. This year we’ve counted 23, a bit below the average of 30 from 2006-13. (More on that in a minute.) Most weren’t big news outside the towns where they occurred. Typically, they involved a man targeting family members and acquaintances. Most involved guns but a handful did not. None involved semiautomatic rifles, although police haven’t revealed the weapon in a few cases. Almost half of the suspects were found dead or were killed by police. In all, 104 victims were killed, 12 more wounded. Continue reading