Six things to know about mass shootings in America

What is most alarming with mass shootings is the fact that this increasing trend is moving in the opposite direction of overall intentional homicide rates in the U.S., which decreased by almost 50 percent since 1993 and in Europe where intentional homicides decreased by 40 percent between 2003 and 2013.

#3: Restricting sales works
Due to the Second Amendment, the United States has permissive gun licensing laws. This is in contrast to most developed countries, which have restrictive laws.

According to a seminal work by criminologists George Newton and Franklin Zimring, permissive gun licensing laws refer to a system in which all but specially prohibited groups of persons can purchase a firearm. In such a system, an individual does not have to justify purchasing a weapon; rather, the licensing authority has the burden of proof to deny gun acquisition.

By contrast, restrictive gun licensing laws refer to a system in which individuals who want to purchase firearms must demonstrate to a licensing authority that they have valid reasons to get a gun – like using it on a shooting range or going hunting – and that they demonstrate “good character.”

The type of gun law adopted has important impacts. Countries with more restrictive gun licensing laws show fewer deaths by firearms and a lower gun ownership rate.

#4: Background checks work
In most restrictive background checks performed in developed countries, citizens are required to train for gun handling, obtain a license for hunting or provide proof of membership to a shooting range.

Individuals must prove that they do not belong to any “prohibited group,” such as the mentally ill, criminals, children or those at high risk of committing violent crime, such as individuals with a police record of threatening the life of another.

Here’s the bottom line. With these provisions, most U.S. active shooters would have been denied the purchase of a firearm.

#5: Not all mass shootings are terrorism
Journalists sometimes describe mass shooting as a form of domestic terrorism. This connection may be misleading.

There is no doubt that mass shootings are “terrifying” and “terrorize” the community where they have happened. However, not all active shooters involved in mass shooting have a political message or cause.

For example, the church shooting in Charleston, South Carolina in June 2015 was a hate crime but was not judged by the federal government to be a terrorist act.

The majority of active shooters are linked to mental health issues, bullying and disgruntled employees. Active shooters may be motivated by a variety of personal or political motivations, usually not aimed at weakening government legitimacy. Frequent motivations are revenge or a quest for power.

#6: Historical comparisons may be flawed
Beginning in 2008, the FBI used a narrow definition of mass shootings. They limited mass shootings to incidents where an individual – or in rare circumstances, more than one – “kills four or more people in a single incident (not including the shooter), typically in a single location.”

In 2013, the FBI changed its definition, moving away from “mass shootings” toward identifying an “active shooter” as “an individual actively engaged in killing or attempting to kill people in a confined and populated area.” This change means the agency now includes incidents in which fewer than four people die, but in which several are injured, like this 2014 shooting in New Orleans.

This change in definition impacted directly the number of cases included in studies and affected the comparability of studies conducted before and after 2013.

Some researchers on mass shooting, like Northeastern University criminologist James Alan Fox, have even incorporated in their studies several types of multiple homicides that cannot be defined as mass shooting: for instance, familicide (a form of domestic violence) and gang murders.

In the case of familicide, victims are exclusively family members and not random bystanders.

Gang murders are usually crime for profit or a punishment for rival gangs or a member of the gang who is an informer. Such homicides don’t belong in the analysis of mass shootings.

Editor’s note: this piece was updated on Oct. 2, 2017. It was originally published on Dec. 3, 2015. Frederic Lemieux is Professor of the Practice and Faculty Director of the Master’s in Applied Intelligence, Georgetown University. This article is published courtesy of The Conversation (under Creative Commons-Attribution / No derivative).