Overall gun crime is down, but the data on mass shootings are murkier.
The frequency of mass shootings is a uniquely American problem.
But be careful when you hear reports that say how often such shootings happen. They are not well-tracked by federal agencies, and the definition of a “mass shooting” varies so widely among public researchers that the numbers can be confusing.
One commonly cited database, run by Mother Jones magazine, says there have been four mass shootings in America this year.
Those four incidents occurred at a church in Charleston, S.C. (nine victims killed); a military recruitment center in Chattanooga, Tenn. (five victims killed); a community college in Roseburg, Ore. (nine victims killed); and now at a holiday party in San Bernardino on Wednesday (14 victims killed).
But another commonly cited source for mass shootings, the crowd-sourced Mass Shooting Tracker database, said that as of Friday there had been 353 mass shootings in the U.S. this year.
That would mean we're averaging more than one mass shooting a day.
Here's the difference: Mother Jones counts a mass shooting as any incident in which a lone gunman kills at least four people in a public place, while also excluding gang violence.
But the Mass Shooting Tracker — which is built by members of the social-sharing site Reddit, and which uses news reports as sources — defines a mass shooting as any incident, anywhere, in which at least four people are shot, but not necessarily killed.
Under this definition, Connecticut's 2012 Sandy Hook Elementary School massacre, in which 26 students and staff members were killed, would hypothetically count the same as a shooting in which four people are shot and wounded in a personal dispute at a house party, even if the injured victims were not the intended targets.Huizhong Wu writes at Mashable:
Other definitions, however, draw a more detailed picture.
Data suggest a upward trend in the frequency of mass shootings. A study conducted byresearchers from Harvard's School of Public Health and Northeastern University found that the frequency of mass shootings has tripled since 2011; a more detailed 2014 FBI analysis shows an uptick in active shooter situations, or incidents in which "an individual [is] actively engaged in killing or attempting to kill people in a confined and populated area." However, that data should be read with a caveat.
The Harvard/Northeastern study relied on a definition of mass shooting which excluded domestic violence incidents. They looked only at incidents in which the shooter and victims did not know each other, and in which the shooter murdered four or more people.
