A Tally Of Mass Shootings In The U.S.

The shooting in San Bernardino, Calif., was the 355th mass shooting in the U.S. this year — or more than one per day on average so far in 2015 — according to groups monitoring such attacks in recent years.

The San Bernardino case, where 14 people were killed, wasn't the only mass shooting on Wednesday. A 34-year-old woman was killed and three males, ages 17 to 52, were injured by gunfire in Savannah, Ga., earlier in the day. Police believe at least two shooters were involved in that incident, but no arrests had yet been made.

One common definition of a mass shooting is four or more people killed or injured (and that's what we're using for the purposes of this article). Here are some key figures compiled by groups such as ShootingTracker.com, Gun Violence Archive and Everytown for Gun Safety.

462: The number of people killed so far this year in mass shootings. The injury toll is 1,314. The shootings have taken place in 47 separate states.

3 Years: The San Bernardino shooting is the deadliest since the 2012 massacre at Sandy Hook Elementary School in Newtown, Conn., which claimed the lives of 20 students and six adults.

281: The number of mass shootings last year. There's debate on how rapidly the rate of such attacks has been rising because the numbers can look very different depending on the standard that's being used.

The definition of four or more killed or injured has been used only in recent years by private research groups, which rely on media reports. The Congressional Research Service tracks shooting cases in which four or more people are killed and, by that standard, the annual figure has tended to range only slightly, from about 20 to 22 cases per year from 1999 to 2013. Some observers say this shows that the number of mass shootings has been a chronic problem for many years, and that the only real change is the amount of media attention they receive.

57: The percentage of cases in which a current or former partner or family member was among the victims. Women account for 50 percent of the victims in mass shootings, compared with only 15 percent of overall gun homicides, according to Everytown for Gun Safety, based on media reports from 2009 through July.

2 out of 160: The number of mass shootings that involved more than one gunman, according to an FBI report released last year, covering the period from 2000 to 2013.

Around 11,000: Roughly the annual number of gun-related homicides in the U.S. The figure has been declining gradually over the past two decades. The vast majority of gun deaths are not mass shootings, which account for well under 5 percent of all shooting deaths.

Greg Myre is the international editor of NPR.org. Follow him @gregmyre1