A new FBI study confirms that the number of mass shootings in the United States has increased steadily over the past decade.
The Bureau issued a report Wednesday that identifies 160 active shootings between 2000 and 2013. Active shootings are defined as incidents in which a gunmen fired at a large group of people and killed or attempted to kill more than one person.
The data show that between 2000 and 2007, there was an average of 6.4 active shooter incidents per year, but that from 2007 to 2103, the rate of such incidences more than doubled, to an average of 16.4 shootings annually.
The study did not look at the motives, but it identified some of the common characteristics of the shooters. Most of them were individuals who had grievances or felt marginalized.
Most of the shootings were carried out by one person at a school or business. Most of the school shootings were carried out by students, and only six of the shooters were women.
Officials explain the increase in the number of shootings in recent years as a "copycat phenomenon." They say past shootings and the resulting notoriety inspired new incidents.
More than 1,000 people were killed or wounded in the shootings that have occurred in 40 out of the 50 states.
The study was prepared to help train law enforcement agents in how to respond to such incidents.