What forms of gun control work best? Congress bans federal agencies from finding out.

The federal government is willfully ignorant about guns.

When you don't know enough about something, your reaction is probably to research it — on Google, on Wikipedia, at the library. The federal government is supposed to respond in a similar way when it has questions about certain laws and policies. So if there's a public health crisis, the Centers for Disease Control and Prevention (CDC) is usually charged with looking into the matter by funding studies and research that look into the best policies to deal with the issue.

But there's one thing the federal government won't study, even though it presents a clear public health threat: guns. That's because, starting in 1996, Congress imposed major restrictions on what kind of gun violence research the CDC can do. And the agency has interpreted the restrictions to stop almost all gun-related research.

Now former Rep. Jay Dickey, the Republican congressman who spearheaded the ban, is apologetic about its effects. Following the Umpqua Community College shooting, Dickey told the Huffington Post, "I wish we had started the proper research and kept it going all this time. I have regrets. … If we had somehow gotten the research going, we could have somehow found a solution to the gun violence without there being any restrictions on the Second Amendment."

But stopping this kind of research is exactly what pro-gun groups like the National Rifle Association (NRA) wanted when they supported it. 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.

Congress's restrictions stifled gun violence research

Back in 1996, Congress approved a budget restriction that stated, "None of the funds made available for injury prevention and control at the Centers for Disease Control and Prevention may be used to advocate or promote gun control." The ban remains to this day, and it was later extended to the National Institutes of Health (NIH), another federal agency that studies public health issues.

The ban was originally intended to stymie advocacy work in favor of gun control, its supporters say. But the CDC, concerned of any political backlash, effectively halted all significant research on gun violence. And Congress has held the ban in place for the past couple of decades.

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.

One analysis by criminologists John Lott and John Whitley found that total gun research, which includes privately funded studies, has gone up since 1996. But it hasn't kept up with even bigger increases in all other kinds of research, suggesting that the federal ban may suppress some potential studies even if it's not putting an end to all research.

The ban tries to stop federal agencies from treating guns as a public health issue

The restrictions are part of a broader effort to stop the federal government from funding any research that might lead to the treatment of guns as a serious public health issue.

The Bureau of Alcohol, Tobacco, Firearms, and Explosives can't distribute much of its trace data for research purposes, and Obamacare limits doctors' ability to gather data on patients' gun use. And the biggest contention toward Surgeon General Vivek Murthy's nomination in the Senate was that he signed a letter from Doctors for America asking Congress to take "strong measures" to reduce gun violence.

As the Huffington Post explained, pro-gun groups like the NRA worry that any findings from this kind of research would be used to call for new restrictions — or even bans — on firearms. In the 1990s, they characterized research that found having a gun in your house increases your odds of death as propaganda pushing for gun control. (Of course, another way to interpret this scenario is that new evidence would be guiding policy.)

Others simply feel that this research is a waste of the public health agencies' time and money. Speaker John Boehner justified the ban in 2011 by arguing that guns aren't diseases: "The CDC is there to look at diseases that need to be dealt with to protect public health."

Of course, the CDC and NIH study issues that aren't diseases — such as car crashes and pool safety. And that work saves lives by developing a body of evidence and awareness that lawmakers can use to establish new policies.

There are signs of change. After the 2012 mass shooting at Sandy Hook Elementary School, President Barack Obama moved to interpret the ban literally — so it only stops strict advocacy efforts by the CDC, not all gun violence research conducted by federal agencies. But as the Washington Post explained, the CDC remains cautious of acting on Obama's directive, and, as a result, not much federally funded research gets done.

Guns are a big public health issue in America

Regardless of how one feels about the right to bear arms, the research that has been done on firearms is very clear: America has more guns than the rest of the world, and that's leading to tens of thousands of preventable deaths, because more guns means more gun deaths.

If the US had gun death rates comparable to other developed countries, it could save literally tens of thousands of lives. Getting gun death rates down to UK levels, for example, would have saved 32,909 US lives in 2013.

But since America's gun death toll is so high, firearms are linked to more deaths than other things we consider serious public health and safety hazards. Between 2001 and 2013, guns killed more people in the US than AIDS, illegal drug overdoses, wars, and terrorism combined.

At the same time, the empirical research shows that reducing the number of guns — by reducing access to them, or by immediately cutting the supply of them through, for example, buyback programs — would lead to fewer of these gun deaths. "Within the United States, a wide array of empirical evidence indicates that more guns in a community leads to more homicide," David Hemenway, director of the Harvard School of Public Health's Injury Control Research Center, wrote in Private Guns, Public Health.

But to decide how to reduce access to guns and the actual supply of them, there needs to be more research on the best policies. Would a buyback program work in the US? Would limiting high-capacity magazines? What about a ban on certain types of guns, such as assault weapons? No one can answer these questions with total confidence, largely because the federal government's ban on gun violence research has made it more difficult to empirically test what works.

"If there is no research, it is harder to make suggestions for policy reform," Garen Wintemute, director of the Violence Prevention Research Program at the University of California Davis, told the Huffington Post. "And if you have a vested interest in stopping policy reform, what better way to do it than to choke off the research? It was brilliant and it worked. And my question is how many people died as a result."