NEW YORK — More than one a day.
That is how often, on average, shootings that left four or more people injured or dead occurred in the United States this year, according to compilations of episodes derived from news reports.
Including the worst mass shooting of the year that unfolded horrifically on Wednesday in San Bernardino, California, a total of 462 people have died and 1,314 have been injured in earlier shootings, many of which occurred on streets or in public settings, the databases indicate.
It is impossible to know whether the number of such shootings has risen in recent years because the databases go back only a couple of years. And experts fiercely debate whether mass shootings that involve four or more deaths are on the rise. Four or more dead is a standard used by congressional researchers and other experts who study mass killings.
Nonetheless, the stream of shootings this year — including an attack on a Planned Parenthood clinic in Colorado that left three dead last week and a shooting at a community college in Oregon that left 10 dead, including the gunman, in October — has intensified the debate over the accessibility of powerful firearms.
Two databases that track mass shootings — shootingtracker.com and gunviolencearchive.org — depend on news accounts and are not official. Nonetheless, they give an indication of the widespread nature of such episodes. Since January, there have been at least 354 such cases in about 220 cities in 47 states, shootings, according to shootingtracker.com.
In November, six people were killed, five of them shot to death at a campsite in east Texas; 17 people were wounded in a shootout as a crowd watched the filming of a music video in New Orleans; and four died, including twin 5-month-old babies, in an episode of domestic violence in Jacksonville, Florida. So far this week, five people were wounded in a Sunday morning shooting in Kankakee, Illinois, and another shooting Wednesday, before the San Bernardino attack, left one woman dead and three men injured in Savannah, Georgia.
Ted Alcorn, the research director for Everytown for Gun Safety, a nonprofit organization that advocates gun control, said the shootings with multiple victims were just a small subset of everyday gun violence in America.
“You have 14 people dead in California and that’s a horrible tragedy,” he said. “But likely 88 other people died today from gun violence in the United States.”
In studying shootings that left four or more dead from 2009 to mid-2015, his organization found certain patterns. In only 11 percent of cases did medical, school or legal authorities note signs of mental illness in the gunmen before the attack, the organization said.
Domestic violence figured strongly: In 57 percent of the cases, the victims included a current or former intimate partner or family member of the shooter. Half of all victims were women.
More than two-thirds of the shootings took place in private residences; about 28 percent occurred in public spaces, the study found.
More than 60 percent of the attackers were not prohibited from possessing guns because of prior felonies or other reasons. But the study still found there was less likelihood of mass killings in states that require background checks for handgun sales than in states that do not — and even less chance of shootings by people who were prohibited by law from possessing firearms.
In a recent report, the Congressional Research Service found a slight uptick in shootings in which four or more victims died. The report found an average of 22.4 mass shootings a year from 2009 to 2013, compared with 20.2 shootings in the previous five years.
But James Alan Fox, a criminologist at Northeastern University, said his research showed the number of such shootings has roughly held steady in recent decades.
He said that if you also included the data for 2014 from the same source that CRS used, and look at recent four-year intervals instead of five-year intervals, then the average number of annual mass shootings actually declined slightly from 2011 to 2014, compared with the previous four-year period.
“It’s a matter of how you slice it,” said Fox, who praised the CRS report.
While the numbers shift from year to year, there has been no discernible trend either in the numbers or in the characteristics of the assailants, said Fox, who is also a co-author of “Extreme Killing: Understanding Serial and Mass Murder.”
“The only increase has been in fear, and in the perception of an increase,” he said. “A lot of that has been because of the nature of media coverage. In the ’70s and ’80s, we didn’t hear about it on the Internet — because there was no Internet — and we didn’t have cable news channels that would devote 24 hours of coverage.”
The shooting in San Bernardino was unlike nearly every other shooting of its type in the United States in the past decade and a half because it involved more than one gunman and the suspects managed to flee the scene.
Just two of 160 active shooter episodes from 2000 to 2013 had more than one gunman, according to a 2014 report released by the FBI. Only 25 of the gunmen got away without being arrested or killed, or committing suicide.