The best available evidence suggests two major National Rifle Association gun policy prescriptions — what are known as “stand your ground” self-defense laws and permissive concealed carry laws — increase homicides and violent crime.

That is according to a massive new study by the RAND Corporation, an independent think tank. The group's experts scoured thousands of academic papers on gun violence in an effort to make definitive statements about how gun policies affect crime and safety. They winnowed that list down to only the highest-quality studies — just 62 in total — containing evidence capable of establishing a causal link between a gun policy change and a specific outcome.

Because the RAND researchers' criteria for including studies in their final analysis were rigorous, for the majority of policies and outcomes, there was not enough good research to make any definitive statements — a clear indication of how little we  know about how to prevent gun violence. But there were notable exceptions.

There is moderate evidence, for instance, that “stand your ground” laws, which remove the requirement for gun owners to attempt to retreat from a situation before using lethal force, increase total rates of homicide. A 2013 study, for instance, found that states passing such laws saw 6 percent to 11 percent increases in their total homicide rate. Another study found that Florida experienced a significant 24 percent increase in total homicides and 32 percent increase in firearm homicides following enactment of the stand-your-ground law in 2005.

The NRA has been a vigorous champion of these laws. After the shooting of unarmed black teenager Trayvon Martin in 2012, the group released a statement saying stand-your-ground “empowers lawful people to defend themselves, and deters would-be murderers, rapists and robbers,” and “the alternative leaves the innocent in danger.”

RAND's researchers also uncovered limited evidence that on balance, permissive concealed carry laws increase overall rates of violent crime. While studies into the effects of concealed carry on the rates of specific crimes, like murder, armed robbery and rape, were generally contradictory and inconclusive, one recent high-quality study conducted in 2016 concluded that on net, the expansion of concealed carry laws increased violent crime overall. There is also evidence showing that permissive concealed carry laws increase rates of accidental firearm injury.

Again, that runs contrary to the NRA's doctrine of “more guns, less crime.” Recently the group has been heavily involved in the push for a national concealed carry reciprocity bill that would make concealed carry permits issued in one state valid in all other states. It also supports legislation that allows gun owners to carry concealed firearms in public without a permit.

The RAND findings diverged from the NRA's preferences in other key areas, as well. For instance, the group has lobbied against laws intended to prevent children from getting their hands on unsecured guns. RAND's researchers uncovered strong evidence that these laws prevent unintentional firearm injuries among adults and children, and that they're effective at preventing suicides, as well.

The NRA also opposes expanding background checks for gun purchases because “background checks don’t stop criminals from getting firearms.” The research compiled by RAND shows moderate evidence that dealer background checks decrease rates of firearm homicide and limited evidence that background checks decrease violent crime and total homicide rates.

One area where the NRA's views are in line with the research is in the realm of mental health. RAND found moderate evidence that mental health-related prohibitions on gun ownership lead to a decrease in violent crime. Following major mass shootings, the NRA typically urges lawmakers to focus their efforts on keeping guns out of the hands of the mentally ill, rather than gun control per se.

All told, the RAND report can be read as an indictment of the gun policy agenda favored by the NRA and its allies in Congress. On balance, the evidence suggests a number of NRA-backed policies, like stand-your-ground laws and permissive concealed carry rules, increase gun violence. Conversely, there is good evidence showing that measures opposed by the NRA, like expanded background checks and child access prevention laws, could reduce the overall toll of gun violence.

Setting individual policies aside, the chief argument of the new RAND report is that there is an urgent need for more, better research into gun violence and how to prevent it. “Many of the possible effects of gun policies that are raised in policy debates have only rarely — or never — been studied rigorously,” RAND's Andrew R. Morral, the project's leader, writes.

The report calls on Congress to eliminate the current restrictions on federal funding for gun research — restrictions that were put in place largely at the behest of the NRA.

The NRA did not respond to a request for comment.