Congressional Research Service Releases Study of Mass Shootings

Jesse Walker, Reason, August 3, 2015

The Congressional Research Service (CRS) has just released a report on mass shootings, drawing on two large chunks of data. The first is the FBI’s series of supplemental homicide reports from 1999 to 2013, as buttressed by various scholars who have done their best to fill the gaps and fix the errors in the police statistics. The second is a dataset assembled by Grant Duwe, a criminologist at the Minnesota Department of Corrections and the author of Mass Murder in the United States: A History. Duwe–who tells me he thinks the CRS “did a really good job”–looks specifically at mass public shootings, and his data go all the way back to 1970. (We’ll get to the distinction between “mass shootings” and “mass public shootings” in a moment.)


Have mass shootings become more common?

Slightly. The average number of mass shootings was a little bit higher in 2009–2013 than in either of the previous five-year periods, and the average number of casualties was more substantially higher. (*) The study attributes both increases essentially to one outlier year, reporting that they “were largely driven by a few incidents in 2012. If 2012 were excluded, the averages would actually have been lower than the preceding five-year period.”

James Alan Fox, an expert on mass murders who teaches criminology at Northeastern University, says the clearest pattern in the study’s data is simply “a great volatility in the numbers. There’s no solid trend.”

Do most of these shootings look like Columbine?

There’s a number of different definitions of “mass shooting” floating around out there, but the CRS report defines it as any gun crime where four or more people are murdered in a single incident. Most Americans process the phrase more narrowly than that: They think of random shootings in schools, at work, and in other public places. The CRS describes these as “mass public shootings,” and it distinguishes them from two other categories: “familicide mass shootings,” in which the murderers kill family members, usually in private spaces or in remote and secluded settings; and “other felony mass shootings,” which are committed in the course of another crime (such as a robbery) or common circumstance (such as an argument that gets out of hand). In theory, these categories can overlap, but the CRS researchers assigned each incident to just one category. (**)

Just as most shootings are not mass shootings, most mass shootings are not public shootings. There have been an average of 4.4 mass public shootings per year since 1999. The figure for familicides is 8.5 and the other-felony count is 8.3.


Using Duwe’s data, the CRS found an increase in the number of mass public shootings since the 1970s: There was an average of 1.1 incidents per year in that decade, 2.7 per year in the ’80s, 4 in the ’90s, and 4.1 in the 2000s. The shootings also became a bit more deadly over the same time period, with ’70s shootings killing an average of 5.5 people per incident and ’00s shootings killing 6.4. (***)

Those are raw totals, without taking population growth into account. If you look at the number of victims per capita, the average has gone up a little from 1970 to today but the numbers are so small that the fluctuations are essentially statistical noise. “Basically, there is no rise,” says Fox, the Northeastern criminologist. “There are some years that are bad, some that are not so bad.”



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