A country where one in three households owns guns is a country where a lot of children grow up alongside deadly weapons. New calculations indicate just how many of those kids live in homes where adults fail to safely store their firearms.

According to the analysis, an estimated 4.6 million American children reside in a household where at least one gun is kept loaded and unlocked. The study’s authors also determined that the share of child-rearing gun owners who don’t secure all their firearms has nearly tripled since the last time similar research was conducted.

The findings were published online on May 10 in the Journal of Urban Health, a little more than a week before a gun rampage outside of Houston provided a horrific illustration of the dangers that arise when firearms are left accessible to children and teens.

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Kids find guns and unintentionally shoot themselves or others. Unsecured firearms are a leading means of youth suicide. As the nation was reminded last Friday, children also sometimes use their parents’ or caregivers’ guns to commit homicides or mass murders: The 17-year-old student charged with fatally shooting 10 and wounding 13 more at his high school in Sante Fe, Texas, on Friday reportedly carried out his attack with a shotgun and revolver belonging to his father. A federal analysis of school shootings released in 2004 found that 65 percent of perpetrators used a gun owned by a relative.

The new numbers on kids and unsafely stored guns are the latest takeaways from the National Firearms Survey of 2015, the most comprehensive examination of American gun ownership in 20 years. Led by Deborah Azrael of Harvard and Matthew Miller of Northeastern University, the inquiry measured a dramatic shift in preferences and behaviors, away from rifles owned for hunting or sport-shooting and toward handguns possessed for self-defense.

Overall, the new analysis shows, more gun owners with children in their homes store all their guns unloaded and locked up (29 percent) than leave at least one firearm loaded and unsecured (21 percent). The authors believe that among some gun owners, a perceived need to keep firepower at the ready may trump safer storage practices. Households where respondents said they own at least one gun for self-defense were nearly 10 times more likely to leave a gun loaded and unlocked than those for whom firearms serve recreational purposes.

“The overall story that we see is rather than movement toward safer storage, we see movement away from safer storage and that is problematic,” Azrael says.

The rise in the number of children living with unsecured guns cannot be explained only by general population growth, Azrael and her co-authors write in their paper. While earlier studies employed methodologies that may have depressed estimates of unsafe storage, correcting for those undercounts does not affect the overall upward trend.

Adult gun owners have adopted more dangerous storage habits while a related idea has taken root. Polls show that over the past two decades, Americans have come to believe that gun ownership increases public safety and that a home with guns in it is a more secure one. This belief has been fed by the political and media arms of the National Rifle Association. It is not supported by scientific evidence. To the contrary: a 2014 review of existing research published in the Annals of Internal Medicine found that access to guns doubles the risk of homicide and triples the risk of suicide.

Separate studies suggest that shootings by children are among the most preventable forms of gun violence. After spending two years poring over existing assessments of gun laws, researchers at the RAND Corporation found that statutes imposing criminal liability on adults who allow their firearms to fall into kids’ hands have consistently reduced both firearm suicides and accidental shootings among young people. The RAND team concluded that child-access prevention laws — or CAP laws, to wonks — were the most effective of the 13 categories of laws they examined.

The NRA generally opposes CAP laws or works to water them down. Currently, 28 states and the District of Columbia have CAP laws in place, though the strength of those laws varies considerably.