CHICAGO (CBS) — Research by of University of Illinois professor has revealed a surprising trend about mass murder in the United States.

Contrary to what you might think, mass murders are not on the rise, according to computer science professor Sheldon Jacobson.

Jacobson said there were 323 such killings – in which four or more people are killed in one incident – between January 2006 and October 2016. The mass killings appeared to be evenly distributed over that time, meaning their rate remained stable over the past decade, and did not spike during any particular season or year.

“The data doesn’t lie. The rate of these events just is not increasing as the perception is given in the media. This is just what it is,” he said.

The professor used a decade’s worth of data from USA Today that was cross-checked by the FBI. He said his analysis also found public shooting sprees like the Las Vegas massacre are not the most common type of mass killing.

“Family mass killings are over three times more likely to occur than a public killing. So what we just saw in Las Vegas is actually not the most common type of mass killing,”

Guns are the weapon used in 75 percent of the killings, ahead of knives and arson.

Jacobson said the research, which is being published in the journal Violence and Victims, shows you can’t predict a mass murder based on information from an earlier one.

He said, because they’re so unpredictable, the best way to prepare for something like that is not to station police officers in all public places, but to train them really well in rapid response.