The mass shooting in Las Vegas last week — like every high-profile mass shooting — raised a host of questions about why such horrors happen and how they can be prevented. But don’t look to Congress to help provide the answers.

Could gunman Stephen Paddock have been stopped while he was stockpiling dozens of weapons ahead of his rampage if law enforcement officials had tracked and flagged suspicious gun purchasing patterns?

How many of the 58 victims lost their lives — and how many hundreds were injured — because Paddock used specialized devices and high-capacity magazines that allowed him to spray almost continuous fire?

Where did Paddock buy his guns and equipment, and did he frequent retailers that have sold weapons used in other crimes?

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Questions like these could be clarified by federally funded research. But many lawmakers, swayed by arguments from gun rights groups, have for decades muzzled gun control data collection and research that could help curb gun violence and mass shootings, political scientists and public health experts say.

Those limitations are unmatched in other fields. While federally funded research has made huge strides in understanding addiction, disease and auto safety, majorities in Congress have shown little interest in encouraging gun studies, even in the aftermath of previous mass shootings.

Answers needed?

“It’s a national embarrassment that we don’t know in any detailed way the answers to so many of the major questions you need to really tackle this problem,” said Alan Leshner, CEO-emeritus of the American Association for the Advancement of Science, or AAAS. “Gun violence is not something you can solve by just intuition and common sense or ideology.”

Numerous policies and budget decisions discouraging gun-related research have originated in Congress in the past 20 years, and few — if any — have been relaxed.

The clampdown started with an amendment to an appropriations bill in the mid-1990s that prohibited the Centers for Disease Control from “engaging in any activities to advocate or promote gun control.” The  “Dickey amendment,” named after former Republican Rep. Jay Dickey of Arkansas, a vocal opponent of gun control, has since been continued in every fiscal year.

While the measure did not expressly address research, it came on the heels of National Rifle Association outcry over CDC-sponsored research on the correlation between guns kept in homes and homicides.

To drive the message home, Congress also stripped the CDC of $2.6 million of its budget — the same amount that it had allocated to gun research the previous year — and earmarked the money for traumatic brain injury.

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Gun rights groups and some conservative media call the CDC research “openly biased” and say the number of gun-related journal articles has remained constant in the years since. The NRA did not respond to a request to comment for this article.

Gun control groups, on the other hand, argue that while they do want more research, it is past time for more studies.

“We know how to solve this problem, so I’m a little wary of the idea that we should just set up a commission to study it for the next few years,” said Avery Gardiner, co-president of the Brady Campaign to Prevent Gun Violence.

A CDC spokeswoman said the Dickey amendment does not prohibit the CDC from collecting public health data on firearm violence.

“CDC has and continues to support data collection activities and analyses to document the public health burden of firearm injuries in the U.S.,” spokeswoman Julie Eschelbach said in an email.

But scientists got the message that they could lose funding — or their jobs. Both the American Medical Association and the American Psychological Association have published articles about the research freeze.

The big chill

The chilling effect was so profound that the CDC did not resume its gun-related work even after President Barack Obama ordered it to in the aftermath of the 2012 mass shooting at an elementary school in Newton, Connecticut, Leshner said.

Leshner, then the chief executive of AAAS, chaired a committee convened at the CDC’s request after Obama’s directive to identify high-priority areas of research that would improve the understanding of what causes firearm violence and how to prevent it. None of the proposals in the resulting 62-page report have been implemented, he said. Congress also did not appropriate the $10 million that Obama requested for CDC research.

Other agencies have faced roadblocks as well. Congress extended the Dickey restriction to all Department of Health and Human Services agencies in 2012, under intense pressure from the gun industry after the National Institutes of Health funded a study that found that people who carry guns are four times more likely to be shot in an assault than those who are unarmed.

After the Obama directive the following year, however, the NIH began funding new studies. But it allowed the program to lapse this year, after funding 22 projects for $18 million, Science magazine reported in September.

Lawmakers have also placed restrictions on what kinds of data is collected and released by the Bureau of Alcohol, Tobacco, Firearms and Explosives, or ATF, the agency tasked with monitoring gun licensing and sales.

Those restrictions include a law passed by Congress in 1986 that prohibits the agency from computerizing records of gun owners and sales, meaning employees have to sort through thousands of paper and microfilm records to trace guns used in crimes and terror attacks — the same way they would have in the 1970s.

Another amendment attached to Department of Justice appropriations bills since 2004, named after former Republican Rep. Todd Tiahrt of Kansas, restricts what kind of firearm tracing data the ATF can release. As the rule now stands, the ATF can release complete data only to domestic and foreign law enforcement, although aggregated statistics may be released to the public.

David Chipman, a former ATF special agent who is now a senior policy adviser at Americans for Responsible Solutions, said the agency has also struggled with chronic underfunding. The agency is tasked with monitoring the country’s tens of thousands of licensed gun dealers. It is only slightly bigger than the Washington, DC, police department.

“There is an enormous misconception that our gun laws are strong, comprehensive and overly restrictive,” he said. “In my 25 years of experience, our gun laws are riddled with holes, difficult to enforce and are not contributing to public safety.”

Americans for Responsible Solutions was launched by former Arizona Rep. Gabrielle Giffords and her husband, retired Navy captain and astronaut Mark Kelly, after Giffords was shot in the head during a mass shooting at a constituent meeting in her district.

Congress’ own in-house think tank, the Congressional Research Service, has pointed out shortcomings in federal data. A 2015 report analyzing the previous 15 years of mass shootings found that Congress could take action to help lawmakers craft better policies.

Congress could encourage improvements to the data sets maintained by the FBI and the CDC. It could require the comprehensive and unbiased collection and release of ATF data on the legality of firearms transfers. It could direct the ATF and the Bureau of Justice Statistics to make annual reports to Congress about the frequency and deadliness of multiple-victim homicides, and how the offenders acquired the guns they used. It could encourage the creation of an “authoritative and comprehensive” data set of the types of firearms used in mass shooting incidents, along with the number of reloads and shots fired.

Academics point out that important national research is still getting done, including work funded by theNational Institute of Justice, media companies or private institutes and universities. Recently, the state of California spent $5 million to start the country’s first public research center devoted to gun violence at the University of California.

“It is an outrage that the CDC and the federal government puts so little money into what is an important issue in terms of our standard of living, public health, community development,” said Philip J. Cook, a Duke University professor and former consultant to the Justice and Treasury departments. “That doesn’t mean nothing is happening.”

He said privately funded research is “vibrant and rigorous.” He cited recent groundbreaking studies of concealed carry laws, the effects of mandatory waiting times on homicide and suicide rates, and the connection between mass shootings and domestic violence.

But there is no match for the scale of federal resources, and the clout that the rigorous federal peer review process brings to a project, said Garen Wintemute, an emergency physician and the director of the violence prevention research program at the University of California, Davis.

Some research has produced controversial conclusions.

A Department of Justice-funded study in 2004, for example, found that a 1994 ban on assault weapons had had only “mixed” success. The findings were used to justify sunsetting the ban that year.

Last week, Leah Libresco, a statistician and former news writer at data journalism site FiveThirtyEight, wrote in The Washington Post that her experience spending three months analyzing all 33,000 lives ended by gun violence every year had changed her mind about what interventions would help combat gun violence.

“The best ideas left standing were narrowly tailored interventions to protect subtypes of potential victims, not broad attempts to limit the lethality of guns,” she wrote.

More unbiased research is needed, academics said.

“The more scholarly, objective scientific research on a topic increases the likelihood that policy that would enact is sound,” said Kristin Gross, a Duke University professor and co-author, with Cook, of “The Gun Debate: What Everyone Needs to Know.”

The more research available, Gross said, the healthier the debate.

Research can change minds. Even in Congress.

Late in life, Dickey, the congressman whose namesake measure was responsible for shutting down gun research at the CDC, became friends with Mark Rosenberg, the former director of the CDC’s National Center for Injury Control and Prevention.

The two men were considered archrivals in the 1990s. But Dickey became convinced by Rosenberg’s argument that traffic fatalities had diminished after federal studies recommended the use of seat belts, air bags, guardrails and other measures.

Before Dickey’s death last spring, the two men wrote several op-eds together calling for more research they said would “protect gun rights while reducing the toll of gun violence.”

California lawmakers, at least, have been convinced by such arguments.

When they were considering using taxpayer money to pay for firearm violence center within the University of California system — a measure prompted in part by the 2015 San Bernardino shootings — the bill’s sponsor, Democratic state Sen. Lois Wolk, came to the hearing with a letter of support from Dickey.

She would read a passage after every objection, saying, “On that point, I have a letter from Congressman Jay Dickey,” said Garen Wintemute, the director of the research program in California.

“It was quite effective that she had the architect of the original ban on funding for research on her side,” he said.

So far, proposals for gun violence studies have been overwhelmingly supported by Democrats. House minority leader Nancy Pelosi last week called on Speaker Paul Ryan to create a commission to examine gun violence, similar to a proposal in a bill introduced in May by California Rep. Mike Thompson.

But some influential Republicans and moderate Democrats who have NRA support have also called for more research.

Notable examples include Sen. Charles Grassley, who sponsored an amendment after the Orlando shooting last year, calling for research on the causes of mass shootings and increased funding for the federal background check system.

Grassley has also proposed legislation that would authorize studies into the correlation between video games and violence, a proposal endorsed by the National Academies of Science. His office did not return a request for comment last week.

“The worst enemy we all face is the idea of fatalism, that we’re just locked into this deadly standoff between gun rights and gun control people and that’s not true at all,” Rosenberg said.

Rosenberg said he believes lawmakers and government officials could be convinced that the only way to both protect Second Amendment rights and improve public safety is through science. He added that he hopes Congress leaves the Dickey amendment in place, as an assurance that gun rights will be protected.

“We put congressmen and senators in a terrible position when we ask them to vote on laws when we don’t know whether they are safe or effective,” he said.