Depending on whom you ask, there have been 353 mass shootings in the United States this year, or four. Or some other number in between.
How can the figures be so far apart?
A mass shooting would seem to be self-evident. But with the highly politicized debate over gun control, and no fixed standard, there's an ongoing battle over the definition. Some say mass shootings are soaring, while others point to numbers suggesting they have been at roughly the same level for years.
The high-end number of 353, widely cited this week in the wake of the San Bernardino shooting, comes from the private research group ShootingTracker.com. Several similar groups have emerged in recent years and have set their own parameters for a mass shooting, defining it as any instance where four or more people are killed or wounded by gunfire.
"This entire debate is ridiculous. A shooting is a shooting," German Lopez wrote in Vox as he argued in favor of the bigger number. "The broader problem is that the U.S. has levels of gun deaths that are far beyond what any other developed country deals with — even though we know that gun control policies could help bring down the number of gun deaths."
The low-end number, which comes from Mother Jones magazine, is based on a traditional FBI definition, dating back decades, which describes a mass shooting as a case where four or more people are killed in an indiscriminate attack in a public place.
The magazine has long followed this subject, maintaining a detailed database that goes back to the early 1980s. It lists the four mass shootings this year as the San Bernardino killings, the October community college shooting in Oregon (nine dead), the July attack on a military recruiting center in Tennessee (five dead) and the June church shooting in South Carolina (nine dead).
What about last month's shooting at the Planned Parenthood clinic in Colorado, where three people were killed and several injured?
Mother Jones doesn't include that, since fewer than four people were killed. It also excludes cases like family disputes that take place inside a home, even if four or more people are fatally shot.
"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," Mark Follman, the national affairs editor at the magazine, wrote in an op-ed in The New York Times.
"Everyone is desperate to know why these attacks happen and how we might stop them — and we can't know, unless we collect and focus on useful data that filter out the noise," he added.
The government has tweaked its own standard. In the aftermath of the 2012 killings at the Sandy Hook Elementary School (26 dead), Congress lowered the threshold for a mass shooting to three deaths.
Yet adopting this measure makes it hard to accurately compare new data with old data that used four deaths as the benchmark.
Partisans can pick and choose the numbers that best suit their preferences.
Those favoring gun control tend to gravitate to the larger numbers, saying this demonstrates the full spectrum of gun violence, from the deadliest and most sensational cases like San Bernardino, to local crime stories, like a shooting in Savannah, Ga., that also took place on Wednesday and left one woman dead and three men wounded.
Strong supporters of gun rights tend to point to the lower numbers, saying there's no value in lumping together shootings with disparate motives, such as gang violence, drug feuds and bank robberies that turned violent.
No Government Research
The Centers for Disease Control and Prevention (CDC) used to study gun violence. But in 1996, Rep. Jay Dickey, a Republican from Arkansas, effectively de-funded that effort.
Dickey, a life member of the National Rifle Association, is no longer in Congress. But three years ago, he wrote an op-ed in The Washington Post with Mark Rosenberg, former director of the CDC, and expressed a change of heart when it came to studying the topic.
"We were on opposite sides of the heated battle 16 years ago, but we are in strong agreement now that scientific research should be conducted into preventing firearm injuries and that ways to prevent firearm deaths can be found without encroaching on the rights of legitimate gun owners," Dickey and Rosenberg wrote.
President Obama has sought funding in recent years, but has been turned down by Congress.