That rate works out to about one active shooting incident every 18 days.
There's a considerable amount of overlap between "mass shootings" and "active shooter incidents." Mass shootings are generally defined by the number of people killed or injured. Active shooter incidents, on the other hand, are defined only by attempts to kill or wound people.
In May, for instance, a man walked into a Walmart in Grand Forks, N.D., and began shooting. He killed one employee and wounded another before turning the gun on himself. This incident wouldn't qualify as a mass shooting under even the broadest definition used, which uses four people injured or killed as the threshold. But the Walmart shooting was an active-shooter incident, according to the FBI's criteria.
In response to the Orlando shooting, the National Rifle Association recently proclaimed that "the increase in mass shootings is a much hyped myth." But regardless of how you choose to define these shootings — whether you look at mass shootings as loosely or strictly defined, or whether you follow the FBI's lead and look at active-shooter incidents instead — the numbers unequivocally show that these shootings are becoming more common.
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