Newsrooms have been quick to claim that there have been 355 mass shootings in America so far this year, but they've ignored that this statistic comes from an anonymous Internet group with an entirely arbitrary definition of "mass shooting."

"The statistics now being highlighted in the news come primarily from shootingtracker.com, a website built by members of a Reddit forum supporting gun control called GunsAreCool," Mother Jones national affairs editor Mark Follman wrote in an article published this week by the New York Times.

Rather than lean on figures compiled by official federal law enforcement sources, the "shooting tracker" is comprised entirely of news clippings collected from around the Internet by Reddit users.

And the tracker isn't picky.

It "aggregates news stories about shooting incidents — of any kind — in which four or more people are reported to have been either injured or killed," Follman reported.

By including persons who were injured by firearms, the Reddit group inflates the number of "mass shootings" in 2015 to more than 350. In contrast, Mother Jones' own in-depth investigation of the issue turned up just a handful of examples for 2015.

"[T]here have been four 'mass shootings' this year, including the one in San Bernardino, and at least 73 such attacks since 1982," Follman wrote.

Mother Jones' work is based on the Federal Bureau of Investigation's definition "mass shooting," which requires three or more fatalities.

"When we began compiling our database in 2012, we used that criteria of four or more killed in public attacks, but excluded mass murders that stemmed from robbery, gang violence or domestic abuse in private homes," Follman explained, adding that they updated their methods after the federal government revised its standard to three fatalities.

"Our goal with this relatively narrow set of parameters was to better understand the seemingly indiscriminate attacks that have increased in recent years," he added.

So where did the fervently anti-NRA Reddit group get its criteria for "mass shooting?" The founder of the "shooting tracker" project, a person who goes by the name "Billy Speed," told Follman he made it up himself.

"Three years ago I decided, all by myself, to change the United States' definition of mass shooting," he said.

Along with Speed's arbitrary method for defining the issue, some of the group's "mass shootings" don't quite live up to the title.

One such example includes a story, titled by the group as "4 shot outside Jersey City housing complex." The story is about two boys, one 11-years-old and the other 12-years-old, who had shot a pellet gun at four people.

And this is just one of the many questionable examples included in the group's list of the more than 350 "mass shooting" events for 2015.

Other examples include gang violence, robberies and police shootouts where bystanders were injured, but no one was killed.

"While all the victims are important, conflating those many other crimes with indiscriminate slaughter in public venues obscures our understanding of this complicated and growing problem," Follman noted.

But despite that the data cited by the "shooting tracker" includes questionable examples of "mass shootings," and despite that the group's own definition of the issue is completely made up, major newsrooms in the United States have unflinchingly repeated the 355 figure as it were a stone cold fact.

The statistic was repeated this week as the Washington Post, Fusion, the Los Angeles Times, the Boston Globe, Vox.com, the Huffington Post, PBS Newshour, MSNBC.com and many others lamented that a deadly shooting spree in San Bernardino, Calif., Wednesday marked yet another grim milestone in the United States' ongoing problem with gun violence.

"The San Bernardino shooting is the second mass shooting today and the 355th this year," read a Post headline.

The Boston Globe reported, "There have been more mass shootings this year than days."

The Huffington Post followed with a headline reading, "There Have Been More Mass Shootings This Year Than There Have Been Days," adding, "355 mass shootings in 336 days ... and counting."

The tracker itself is not entirely useless, Hollman noted, but its imprecision threatens to make an already confusing issue even murkier. And newsrooms would do well to consider it as more of a tool than a definitive source, he said.

"There is value in collecting those stories as a blunt measure of gun violence involving multiple victims. But as those numbers gain traction in the news media, they distort our understanding. According to our research at Mother Jones — subsequently corroborated by the F.B.I. — the more narrowly defined mass shootings have grown more frequent, and overwhelmingly involve legally obtained firearms," he wrote.

"Experts in the emerging field of threat assessment believe that this is a unique phenomenon that must be understood on its own," Follman said, adding that the tracker more than anything else underscores the need for better gun violence data.