Wrangling and Pivoting on U.S. Mass Shootings Data


Quick index

As of October 2017, MoJo has maintained a spreadsheet with 91 mass shooting incidents. What does it count, what does it miss, and how does that affect data analysis?

Data/technical links

Mother Jones counts something it finds interesting

The morning after a dozen people were killed in the 2012 Aurora rampage, Mother Jones published a feature purporting to map “26 Mass Murders Across America in 30 Years (Internet Archive version)”. The lede:

It’s perhaps too easy to forget how many times this has happened. The horrific mass murder at a midnight screening of The Dark Knight Rises in Aurora, Colorado, on Friday is the latest in an epidemic of such gun violence over the last three decades. Since 1982, there have been at least 26 mass murders across the United States. We have mapped them below, including details on the shooter’s identity, the date of the event, and the number of victims injured and killed.

The 3 criteria for inclusion:

  • “…carried out by a lone shooter (except in the case of the Columbine massacre, which involved two shooters).”
  • “…happened during a single incident and in a public place”
  • “…took the lives of at least four people”

My 11:30PM, Mother Jones and its readers had identified several more mass shootings to include, along with other caveats:

Editor’s note, 11:30pm PDT: Thanks to all our great readers for the comments, and for flagging several other mass murders that fit the above criteria. We will update the map data soon to include the Xerox killings in Hawaii, the Westside Middle School killings in Arkansas (involving two shooters, like Columbine), the Trolley Square killings in Utah, and the Northern Illinois University killings. (We chose not to include Mark O. Barton in Atlanta, Richard Baumhammers in Pittsburgh, or the Red Lake reservation massacre in Minnesota, whose perpetrators are classified as spree killers.)

Mother Jones continues to count

In December 2012, several months after their breaking news map/feature on Aurora, Mother Jones published a long-form analysis which found 62 mass shooting incidents since 1982: More Guns, More Mass Shootings—Coincidence?.

What is a Mass Shooting?

Questions about Mojo’s mass-shootings data

  • Why count only sole-shooters?
  • How is single-incident counted?
  • How is mental illness tracked?