In this Monday, Oct. 2, 2017 file photo, drapes billow out of broken windows at the Mandalay Bay resort and casino on the Las Vegas Strip, following a deadly shooting at a music festival in Las Vegas. Two hotel employees had called for help and reported that gunman Stephen Paddock sprayed a hallway with bullets, striking an unarmed security guard in the leg, several minutes before Paddock opened fire from the resort on a crowd below at a musical performance, killing dozens of people and injuring hundreds. (Photo: AP/John Locher, File)

By most accounts, random mass killings by gun have grown increasingly frequent since the turn of the millennium, from Columbine in 1999, to the Virginia Tech attack in 2007, to the Newtown school shooting in 2012 and through to the Las Vegas massacre earlier this month. 

But the statistics over the last decade point to a routine, if grim, reality: the rate of mass killings has remained completely steady. At the same time, it remains completely unpredictable, report two scientists at the University of Illinois at Urbana-Champaign in the journal Victims and Violence.

“The evidence suggests there’s a steady rate, and it’s also very unpredictable,” said Sheldon H. Jacobson, one of the authors, a computer scientist. “It’s a challenging combination. You know it’s going to happen—you just don’t know when.”

Jacobson and colleague Douglas M. King crunched the numbers on 323 events from 2006 to 2016, as compiled in a database by USA Today.

But the general conception of mass killings, as defined by the FBI’s definition of four or more victims, only focuses on a minority of the events. For instance, massacres such as the Las Vegas slaughter three weeks ago only make up about 16 percent of the total mass killings. The real driver is familicide, which accounts for 53 percent of the killings (another 10 percent are multiple deaths occurring during robberies or burglaries, they report).

The vast majority are committed with a firearm, at 76 percent of all the events counted over the decade. But some 12 percent were multiple stabbing deaths, and another 10 percent were from arson or fire-related events, according to the analysis.

The two scientists mathematically assessed the temporal distribution of the mass killings over the decade, and also the elapsed time between the occurrences.

Contrary to some other analyses, they are uniformly distributed over the time period of the study, suggesting they are not becoming more frequent. The events are also not clustered on the timeline, suggesting they are not linked to each other through societal or psychosocial means.

“We were looking for some kind of patterns, which would help people to prepare, or potentially prevent such events. The data just did not speak to that,” said Jacobson, in an interview with Forensic Magazine today.

The findings are different from—and sometimes buck—some other recent analyses. For instance, a 2014 paper in the FBI Law Enforcement Bulletin found that active shooter events increased from 2000 to 2012. Another paper in PLoS ONE in 2015 found that there was a “contagion effect” that linked and perhaps inspired mass killings and school shootings.

Jacobson said their single set of data indicates that there is no such rhyme or reason to the carnage.

“We’ve just reported what the data said—we don’t have any ulterior motive or agenda,” the computer scientists said.

However, the decade within the 21st century may indeed represent a new world of mass killings. The USA Today numbers show approximately 30 mass killings per year in the United States, as opposed to comparable statistics showing 26 mass killings annually from 1976 to 1999. In the 1960s and earlier, the rate of mass killings was much lower, according to a previous analysis cited in the paper.

Regardless of the circumstances or media coverage of such events, the data indicates a 21st century reality, said Jacobson.

“The data is basically completely independent of how people feel about a situation—be it fear, be it concern of personal well-being,” said Jacobson. “The data is very robust—it just says exactly what has occurred.”