Gun control advocates examined data from January 2009 and 15 July – states that checked for a criminal history had 64% fewer domestic violence shootings

States with background checks for all handgun sales had 52% fewer mass shootings as states with more lax rules, according to a report by reform advocates who examined more than six years of data.

Researchers for Everytown for Gun Safety, a group that supports gun control checks, also found that between January 2009 and 15 July those states that checked for a criminal history in buyers had 64% fewer mass shootings related to domestic violence.

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More than one in three of the gunmen in mass shootings had a history of felonies, domestic violence or mental illness that should have prohibited them from owning a gun, according to the gun control group.

The researchers relied on the FBI’s definition of a mass shooting – an incident in which at least four people are murdered by a gun – and found 133 such shootings in the six years and seven months of the analysis. They also controlled for population differences between states when accounting for percentages.

The website Shootingtracker.com uses the less conservative definition of four people shot, but not necessarily killed, and has tallied more than 1,000 mass shootings since the December 2012 Sandy Hook shooting, when a gunman murdered 26 people, mostly children, at an elementary school in Connecticut.

Seventeen states and Washington DC require background checks on all handgun sales; two states, Colorado and Washington, expanded checks during the six years relevant to the report.

Several states had no mass shootings by the FBI’s definition during this span, including Rhode Island, New Jersey, Hawaii, New Hampshire and Alaska, illustrating the variation between gun violence rates compared to the report’s findings. Alaska has the highest rate of gun violence in the US, for instance, and does not require background checks for handguns, but more than 80% of incidents are suicides, according to the CDC .

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Similarly, Mississippi ranks fourth for most gun violence in the US and does not require checks, but had no mass shootings by the FBI’s definition. In contrast, Illinois, which requires background checks and ranks better than most of the country for firearm deaths, had six mass shootings, three by a “prohibited shooter”, according to the report.

California and Texas – the most populous states and one with checks, the other without – had the most mass shooting incidents, each with 12. Three of those 12 in each state were committed by someone who should have been withheld a firearm.

Overall and controlling for population, the report concluded that there were 63% fewer mass shootings perpetrated by “prohibited shooters” in states that required background checks for handguns.

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Background checks were almost expanded in the months after the Sandy Hook shooting, when Barack Obama and a coalition of Democratic and Republican senators brought a bill forward that would close loopholes to purchases at gun shows and online. Republicans and a handful of Democrats stymied the bill in the Senate , frustrating the president and gun control advocates.

Although expanded checks have been raised as a modest control, most recently in the wake of shootings at a church in South Carolina and a college in Oregon , Congress has not considered the measure since 2013. Activists have however expressed renewed hope that presidential candidates have seriously discussed gun control in debates, the first time since the 2000 election .

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The gun control group made special note of the link between domestic violence and shootings, finding that there were 59 such shootings in states without background checks for all handgun sales and only 17 in states with full checks.

Gun control advocates have recently called for an expanded ban on firearms for people with any history of domestic abuse . Domestic abuse incidents are five times more likely to be fatal when there is access to a gun, and women are 11 times more likely to be murdered with a gun than in other high-income countries, according to the Law Center to Prevent Gun Violence .

Everytown conceded limits to its study, most notably due to the federal ban on gun research and the ban on publishing data about how and where people bought their weapons. The latter ban prevents non-government employees from learning how many mass shooters acquire weapons, for instance.

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The gun control group also published a second report on gun sales, finding that a few unlicensed sellers account for a disproportionate number of sales in at least one online gun market. Federal law has an “engaged in the business” standard to determine who requires a license to sell, but in practice the standard is arbitrarily or weakly applied in prosecuting cases, the researchers found.

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