Daniel Webster is the director of the Johns Hopkins Center for Gun Policy and Research. Jon Vernick is the center's deputy, and Cassandra Crifasi and Beth McGinty are faculty members at the center.

With the killing of 58 and the wounding of hundreds in Las Vegas last weekend, Americans are once again debating gun violence. Adding to the passion and the entrenched political and economic interests that make this conversation so intense are a number of myths — about how much violence there is, what causes it and how to prevent it. Here are some of the most stubborn ones.

Myth No. 1

Gun violence in the United States is at an all-time high.

Donald Trump accepted the Republican presidential nomination in 2016 with a speech that described a country besieged by violence. He said that President Barack Obama "has made America a more dangerous environment than frankly I have ever seen." Earlier this year, Trump declared the U.S. murder rate to be "the highest it's been in, I guess, 45 to 47 years." Half of Americans in a Pew Research Center poll said gun violence is "a very big problem" today, with 59 percent of non-gun-owners saying the same.

Indeed, data from the FBI indicates an alarming 32 percent increase in the number of homicides committed with firearms from 2014 to 2016. The number of robberies and aggravated assaults committed with firearms increased by 17 percent over that time. The number of people shot in mass shootings has also risen sharply in the past 12 years.

Yet the current rate of firearm violence is still far lower than in 1993, when the rate was 6.21 such deaths per 100,000 people, compared with 3.4 in 2016. The high rate in the early 1990s was linked to a variety of conditions, most notably the emergence of a large and violent market for crack cocaine. It's too soon to determine the causes of recent increases in gun violence or whether the upward trend will continue.

Myth No. 2

Background checks save lives, research shows.

The concept of universal background checks enjoys rare broad support in the debate over gun violence: consistently at or near 90 percent . Large majorities of Republicans and Democrats favor the expansion of background checks to private sales and gun show sales, according to Pew. And there is solid research indicating that laws that keep guns out of the hands of high-risk individuals, such as domestic abusers and people convicted of violent crimes, reduce violence.

But there is no research indicating that background check laws as they currently exist save lives. Studies suggest that the federal Brady Law, which mandates background checks for firearm sales but exempts sales by private parties, has not been strong enough to reduce homicide rates. There is no compelling, peer-reviewed research on the effectiveness of extending background check requirements to private sales — unless those requirements are paired with a permitting or licensing system for purchasers.

Still, state laws requiring checks via a permitting system do reduce the diversion of guns for criminal use, homicides and suicides, and they may lower the risk of police officers being shot in the line of duty. Only 10 states and the District of Columbia require permits for handgun purchasers; eight states require background checks for private sales but do not require permits.

Myth No. 3

Mental illness is behind most gun violence against others.

National opinion polls show that the majority of Americans believe that mental illness, and the failure of the mental-health system to identify those at risk of dangerous behavior, is an important cause of gun violence.

Research says otherwise. Only an estimated 4 percent of violence against others is caused by the symptoms of serious mental illnesses such as schizophrenia and bipolar disorder. Impulsivity, anger, traumatic life events such as job loss or divorce, and problematic alcohol use are all stronger risk factors for gun violence . Research also shows that mental-health-care providers are poor predictors of which patients will go on to harm others. Further, most people with mental illness will never become violent, and most gun violence is not caused by mental illness.

But mental illness is a strong risk factor for firearm suicide, which accounts for the majority of gun deaths in the United States. While improving America's mental-health system would benefit millions of people with mental illness, it would not substantially reduce gun violence against others.

Myth No. 4

Right-to-carry laws decrease crime.

Supporters of right-to-carry laws, which require the issuance of concealed-carry handgun permits to applicants who meet the criteria, often argue that carrying guns makes the public safer: The person with a gun will be able to prevent an attack or take down an active shooter. The economist John Lott wrote in his book "More Guns, Less Crime" that right-to-carry laws are correlated with decreases in violent crime.

Yet the most comprehensive study on the effects of these laws found that violent crime rates increased with each additional year such a statute was in place, presumably as more people were carrying guns. By 10 years after the adoption of a right-to-carry law, violent crime rates were 13 to 15 percent higher than predicted had such laws not been in place.

Additionally, armed civilians are rarely able to deter or interrupt various crimes or even mass shootings. In fact, in zero of the 111 gun massacres analyzed by researcher Louis Klarevas did an armed civilian stop a mass shooting in progress. A separate FBI analysis revealed that unarmed civilians are more than 20 times as likely to end an active shooting than are armed civilians (excluding armed security guards).

Myth No. 5

Mass shootings are random.

High-profile tragedies like those in Las Vegas, where a motive has yet to emerge, and in Aurora, Colo., tend to support the popular notion that mass shootings are random — that there's no connection between the killers and the targets. "Another day, another massacre, and once again it's a gunman targeting strangers in a public place for no obvious reason," read one Washington Post article on a mass shooting at a Louisiana movie theater in 2015.

But most mass shootings are directed at a specific person, group or institution against which the perpetrator has a grievance. A Huffington Post analysis of mass shootings — which the FBI defines as four or more people killed with a firearm, not including the perpetrator — between 2009 and July 2015 found that 57 percent of the incidents involved a perpetrator's current or former intimate partner or a family member, and 70 percent occurred in private dwellings.

While mass shootings in public spaces that kill and wound dozens or even hundreds of people receive plenty of media attention, smaller-scale gun violence occurs with far too much regularity in the United States, claiming nearly 100 lives every day. Most killers, including those who perpetrate mass shootings, aren't trying to murder strangers but are targeting people they know well.

Correction: An earlier version of this story misstated the findings of researcher Louis Klarevas. In his analysis, zero, not four, gun massacres were stopped by an armed civilian.

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