Schools are increasingly becoming fortresses: packed with metal detectors, police officers, and other measures designed to counter the threat of a school shooter. Six states now even require mandatory active shooter drills.

In the wake of the tragedy of the mass shooting at a high school in Parkland, Florida, many local, state, and federal officials are responding by promoting an expansion of these measures — some, including the president, are even calling for arming teachers. One Democratic member of Congress in Georgia even suggested posting the National Guard outside of schools.

But ideally, policy should be proportionate to the danger faced. And that leaves us with a question: Are schools actually increasingly dangerous?

New research released this week by Northeastern University researchers shows that they aren’t.

Criminology professor James Alan Fox and doctoral student Emma Fridel charted the path of mass shootings and school shootings over three decades, from 1992 to 2015. They used a variety of government and nonprofit data sources, including data collected by the FBI, USA Today, and Everytown for Gun Safety, an organization that advocates for gun reform. Their research is the basis of a chapter that will be published in an upcoming book on school violence, “The Wiley Handbook on Violence in Education.”

They found that schools are actually increasingly free of mass shootings, which they define as a shooting in which four or more individuals are killed by firearms. “There is not an epidemic of school shootings,” Fox said in a statement about the research, noting that there were four times as many children shot and killed in schools in the early 1990s as today.

More children are killed every year drowning in pools or in bicycle accidents than in school shootings, Fox added. Over the past 25 years, around 10 students per year were killed in gunfire at school. To put that into perspective, in the fall of 2017, around 56 million students attended public and private public elementary and secondary schools.