The research increasingly suggests that “stand your ground” laws — which expand the reach of self-defense laws to remove a “duty to retreat” in public spaces — cause more homicides and do not reduce violent crime.

Last year, the nonpartisan RAND Corporation released a comprehensive report that found, in part, that “stand your ground” laws are linked to more violent crime, particularly homicides. This month, RAND researchers Andrew Morral and Rosanna Smart published a brief follow-up with some of the new evidence — and “stand your ground” laws now look even worse:

Since publication of RAND’s report, at least four additional studies meeting RAND’s standards of rigor have reinforced the finding that “stand your ground” laws increase homicides. None of them found that “stand your ground” laws prevent violent crime. No rigorous study has yet determined whether “stand your ground” laws promote legitimate acts of self-defense.

“Stand your ground” laws effectively expand the scope of what qualifies, legally, as self-defense. Under standard self-defense laws, someone who’s facing a dangerous threat must retreat if it’s safe to do so, with use of force only legally available as a last resort — what’s called the “duty to retreat.” So through this standard, you can only use deadly force if you cannot safely avoid harm or death by, for example, running away or hiding.

But if a “stand your ground” law is in place, someone can, well, stand his ground, and use up to lethal force even if he can safely retreat while under imminent threat. There are also “castle doctrine” laws, which remove the duty to retreat in a legally occupied setting, such as your home, office, or car (your “castle”). “Stand your ground” is an expansion of “castle doctrine”: While the latter only removes the duty to retreat in your property, the former removes the duty to retreat everywhere — whether you’re in a grocery store, in a park, or on a street.

The laws have become particularly controversial in Florida, where “stand your ground” first passed and subsequently came up after the shootings of Markeis McGlockton and Trayvon Martin.

The NRA has heavily pushed for the laws as part of its broader agenda to loosen access to guns — by making it so people are more able to use their guns without legal repercussions. Its campaign has been very successful: So far, 30 states have enacted “stand your ground” laws.

The RAND report suggests the law has made these states less safe. And it’s not alone in its findings.

A 2016 review of the research, published in Epidemiologic Reviews, found that most big studies looking at “stand your ground” and “castle doctrine” laws found that they actually correlated with increases in homicides. The one study that found “castle doctrine” was associated with reductions in homicides came from a widely discredited researcher. The others found increases in homicides associated with both kinds of laws.

Researchers summarized one of the more recent studies they reviewed: “stand your ground laws were associated with a 6.8% increase in homicide rates, mainly driven by increments (14.7%) in homicide rates among white males.”

Meanwhile, the RAND report found evidence that some restrictions on gun ownership — particularly background checks and child access prevention laws — reduce bad outcomes, including violent crime, suicides, and childhood injuries and deaths.

Again, RAND is not alone there. A 2016 review of 130 studies in 10 countries, published in Epidemiologic Reviews, found that new legal restrictions on owning and purchasing guns tended to be followed by a drop in gun violence — a strong indicator that restricting access to guns can save lives. Several studies have found that, in particular, requiring a license to buy and own a gun is linked to fewer firearm homicides and suicides.

Still, the RAND researchers are very cautious, arguing more research on gun policy is needed in several areas. As Morral told me last year, “Many of the matters that people disagree on when they disagree on gun policy have not been rigorously studied in ways that produce reasonably unambiguous results.”

Morral and Smart explained the root of the problem: “Although approximately 40,000 Americans die annually from gunshot injuries, and two or three times this number sustain non-fatal gunshot injuries, the federal government currently spends a fraction as much on gun violence prevention research as it does on other causes of death that kill similar numbers of people.”

When it comes to “stand your ground” laws, though, we are getting stronger evidence — and it indicates that these laws in particular are dangerous.