Several ideas have surfaced in Washington since the high school shooting in Parkland, Florida, that killed 17 people. Among them: raising the legal age for purchasing assault rifles from 18 to 21, improving the national background check system, and, from President Donald Trump, arming teachers.

Some of them could help. Others might actually make things worse. Unfortunately, we have little evidence about what would actually reduce gun violence and mass shootings like the one in Parkland.

“There’s some evidence that certain types of gun laws, like universal background checks, may be useful,” David Hemenway, a Harvard University professor who has written extensively about injury prevention and guns, told me. “There’s no evidence at all about raising the age to 21. There’s certainly no evidence about arming teachers. There’s evidence [that] arming more people is typically good for the gun industry and bad for society.”

What we do know is that fewer guns likely lead to fewer deaths, as Vox’s German Lopez has explained at length. We do have a few non-government studies, from Connecticut and Missouri, that suggest background checks help reduce gun deaths. A recent RAND survey of the available research primarily argued that more research is needed — but it also found that, from what we do know, limiting access to firearms reduces gun violence.

So improved background checks and higher age limits could reasonably be expected to help. But these are largely inferences from other countries with stronger gun laws rather than rigorously researched theories that have been tested in America.

As for arming teachers, if anything, we would expect that to make the situation worse. More guns tend to breed more violence — whether accidental or intentional.

We don’t know much beyond that. Congress has made it effectively impossible for federally funded researchers to study gun violence. The Centers for Disease Control and Prevention and the National Institutes of Health are the gold standards for public health research in the United States. But they are effectively barred from studying a problem that kills more than 35,000 people in a year.

That represents a significant hurdle to smart policymaking — though advocates of an empirical approach to gun violence argue that shouldn’t stop lawmakers from acting.

“We have to extrapolate from what limited data we have, from different states or countries with different laws. Generalizing from this data is difficult,” Dr. Steven Novella, a professor at Yale Medical School and executive editor at Science-Based Medicine, said in an email. “But we can still craft thoughtful policy based upon the data we have and plausibility. Then track the results of those policies and adjust them as necessary.”

The gun control debate happening in Congress in the wake of the Parkland shooting isn’t about what would work or which policies would actually stop or reduce gun violence. Instead, it’s become about what can pass a Congress disproportionately populated by gun rights ideologues.

There is perhaps no clearer sign of our collective psychosis around the issue of gun control. Proposals are reverse-engineered from political feasibility — despite the fact the Republican majorities are completely out of step with public opinion — even though they may have no basis in empirical research. To make matters worse, Congress perpetuates a status quo that makes it difficult for researchers to even begin to quantify which policies would actually lead to fewer Americans dying violent deaths.

The Dickey Amendment, Congress’s ban on federal funding for public health research on gun violence

Let’s get something out of the way: Gun violence is a public health problem. It is a health risk to tens of thousands of Americans.

“The CDC researches all threats to the health of Americans, and being shot dead is a significant risk to health,” Novella wrote recently. “The CDC also researches deaths from car crashes, and how to mitigate those deaths, for example.”

But there is more or less a federal prohibition on government dollars being spent on public health research about firearms.

It is known as the Dickey Amendment, first approved by Congress in the 1990s. Its effective ban on federal taxpayer money being spent on research that could lead to gun control has since spread from the CDC to the NIH, the federal agencies primarily tasked with protecting the public health. As Vox’s German Lopez wrote back in 2015:

Stopping this kind of research is exactly what pro-gun groups like the National Rifle Association (NRA) wanted when they supported the ban. For decades, the NRA and other gun rights advocates have done everything they can to stop the treatment of firearms as a public health issue — even as these weapons kill tens of thousands of Americans each year. As a result, CDC research funding for gun violence fell by 96 percent between 1996 and 2012, according to Everytown for Gun Safety, which backs gun control. “Major public research funding for gun violence prevention is estimated at $2 million annually,” the group found. “By contrast, in 2011, the National Institutes of Health devoted $21 million to the study of headaches.” The ban doesn’t apply to some agencies, like the National Institute of Justice. But it applies to two big research arms of government, seriously curtailing the amount of money that can flow to studying gun violence. And public health researchers argue it’s stopped more scientists from entering the field, since there’s a good chance they may not be able to get the resources they need to conduct studies on gun violence.

“There’d be a lot more research if there was money,” Hemenway said matter of factly.

More research would mean better ideas for stopping gun violence

This is one of the core causes of that paucity of research that academics lament. We don’t collect all the data we could, and the data we do collect is difficult for researchers to get ahold of, Hemenway said — and all the while top federal researchers have their hands tied.

These prohibitions and obstacles have a real effect on our ability to develop smart gun policies too — and lead to a vicious cycle in which gun rights activists use the lack of strong evidence for gun control against any proposals that would restrict access to guns.

“It seems that those opposed to researching gun violence want to be stuck in a paralysis caused by insufficient information. They can oppose any gun legislation by arguing that there isn’t evidence proving the legislation will work,” Novella wrote. “If that standard were used for all legislation we would have a very different style of government in our country.”

He continued:

Even with our current state of knowledge, we can make rational decisions about gun regulations based on logic, plausibility, and available evidence, then evaluate the outcome and make adjustments. But more importantly, we don’t have to be stuck with our current state of knowledge. We can and should conduct research into the causes and potential solutions to gun violence. It is a health problem for our patients, and it is a public health problem for our society. The medical profession has a legitimate interest in preventing gun violence, and our publicly funded health research institutions should be giving this topic the priority it deserves.

Gun rights hardliners have typically waved away the need for more research. “What works to reduce gun violence is to make sure that criminals are prosecuted and those who have been found to be a danger to themselves or others don’t have access to firearms,” one top NRA official said a few years ago. “Not to carry out more studies.”

But recently, there have been some signs that Republicans might be rethinking their absolute opposition to public health research on firearms. House Judiciary Committee Chair Bob Goodlatte (R-VA) has said the CDC ban should be reevaluated. President Trump’s new health secretary, Alex Azar, has said he wants the agency to conduct these studies and that it might be able to do so without any congressional action.

In the wake of Parkland, it seems like the least Congress or the Trump administration could do. Guns kill tens of thousands of Americans every year. It’s time to treat them like the public health issue that they are.