The federal government’s more restrictive definition means it tends to count fewer incidents than Mass Shooting Tracker. Using 2013, the most recent year for which federal data is available, the Congressional Research Service found 25 mass shooting incidents -- far less than the 363 counted by Mass Shooting Tracker.
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An academic told us that one problem with Mass Shooting Tracker is it lumps together incidents that are different -- for example, those shot in bar fights are counted along with school shootings.
"This is not consistent with the motivations behind events like Columbine, Virginia Tech, Aurora, Tucson, or Sandy Hook, and therefore are not comparable in the way we think of mass shootings," said Jaclyn Schildkraut, at State University of New York System. "By including such events to try and quantify a phenomenon (though the loss of one life is one too many), these sources essentially are inflating the statistics."