The number of shootings in which a gunman wounds or kills multiple people has increased dramatically in recent years, with the majority of attacks in the last decade occurring at a business or school, according to an FBI report released Wednesday.

The study focused on 160 "active shooter incidents" between 2000 and 2013. Those are typically defined as cases in which a gunman in an attack shoots or attempts to shoot people in a populated area.

The majority of the shootings occurred either at a business or school, university or other education facility, according to the study, conducted in conjunction with Texas State University. Other shootings have occurred in open spaces, on military properties, and in houses of worship and health care facilities.

The report was released a day after a man who had recently been fired from his job at a United Parcel Service Inc. (UPS) distribution center in Birmingham, Alabama, shot dead two supervisors at the site before turning the gun on himself.

That ending, with the gunman taking his own life, was a common one in the events the FBI analyzed, with 40 percent of the shooters turning their guns on themselves. Police shot and killed attackers in 13 percent of the cases analyzed.

According to the report, an average of six shooting incidents occurred in the first seven years that were studied. That average rose to more than 16 per year in the last seven years of the study. That period included the 2012 shootings at a movie theater in Aurora, Colorado, and at Sandy Hook Elementary School in Newtown, Connecticut, as well as last year's massacre at the Washington Navy Yard in which a gunman killed 12 people before dying in a police shootout.

The goal of the report, which excluded shootings that are gang and drug related, was to compile accurate data about the attacks and to help local police prepare for or respond to similar killings in the future, federal law enforcement officials said.

"These incidents, the large majority of them, are over in minutes. So it's going to have to be a teaching and training of the best tactics, techniques and procedures to our state and local partners," said James F. Yacone, an FBI assistant director who oversees crisis response and was involved in the report.

A total of more than 1,000 people were either killed or wounded in the shootings studied. The gunman acted alone in all but two of the cases. The shooters were female in at least six of the incidents.

Law enforcement officials who specialize in behavioral analysis say the motives of gunmen vary, but many have a real, or perceived, personally held grievance that they feel mandates an act of violence. Though it's hard to say why the number of shootings has increased, officials say they believe many shooters are inspired by past killings and the resulting notoriety.

"The copycat phenomenon is real," said Andre Simons of the FBI's Behavioral Analysis Unit. "As more and more notable and tragic events occur, we think we're seeing more compromised, marginalized individuals who are seeking inspiration from those past attacks."

Richard Parker, a lecturer at Harvard University's John F. Kennedy School of Government, noted the numbers of mass shootings are minimal compared with the roughly 14,000 murders and 1.15 million violent crimes reported in the United States per year.

"They get more attention than they statistically represent because they are so rare," Parker said. "You have to ask where are the bulk of murders taking place, and this doesn't even qualify as a significant minority. This is a tiny, tiny fraction."

Wire services