Open this photo in gallery Thousands of high school students hold a rally after they walked out of their schools and marched to the state Capitol in Saint Paul, Minn., on March 7, 2018, to protest gun violence and pressure lawmakers to enact stricter gun control. (Glen Stubbe/Star Tribune via AP) Glen Stubbe/The Associated Press

As lawmakers in Washington consider measures to prevent another mass shooting, in one important sense they are groping in the dark.

The debate over guns in America is not only bitter and entrenched but also hobbled by a little known obstacle. For more than two decades, the federal government has purposely restricted funding for studies on gun violence. That means there is a paucity of research into the nature of gun deaths in the country, which in turn impairs the ability to implement effective public policy.

The Trump administration recently released a set of policy proposals in response to the school shooting in Parkland, Fla., last month that left 17 students and teachers dead. The plan encourages states to train certain teachers to carry weapons and establishes a federal commission on school safety. But the White House backed away from a measure it had floated which enraged the National Rifle Association ­ raising the national minimum age to buy a weapon to 21.

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Acting on age limits is a decision for states, U.S. President Donald Trump suggested on Monday. “Things are moving rapidly on this, but not much political support (to put it mildly),” he wrote on Twitter.

Now some legislators are renewing calls to dismantle the barriers facing gun-violence researchers. Chief among them is the 22-year old Dickey Amendment, which has all but frozen gun violence research by the Centers for Disease Control and Prevention, the country’s leading public-health agency.

At a televised meeting at the White House last month, a member of Congress from Florida urged Mr. Trump to support her quest to repeal the amendment. He did not express a view on the issue.

In response, the National Rifle Association and Republican lawmakers tried to eliminate the centre at the CDC that had funded the study. That effort failed, but in 1996, Jay Dickey, a congressman from Arkansas who called himself the NRA’s “point man” in the House of Representatives, succeeded on another front: He enacted an amendment that prevents the CDC from using any funds to “advocate or promote gun control.” At the same time, Congress took the exact amount the CDC was spending on gun research and earmarked it for other use.

While the Dickey Amendment does not, strictly speaking, prohibit research into firearm injuries, the country’s public health establishment got the message. The amendment was a “shot across the bow,” said David Hemenway, director of the Harvard Injury Control Center and the author of the book Private Guns, Public Health. It serves as “a symbol to remind everyone at the CDC that if they do any work about guns, they’re going to get hauled before Congress and beaten up.”

U.S. President Donald Trump will support a modest set of fixes to gun laws, stepping back from some of the more sweeping changes he had considered after the country's latest mass school shooting. Reuters

After the amendment became law, public funding for firearm studies dried up. Researchers scrabbled for funds from universities or private foundations, some of which were also leery of courting political controversy. Garen Wintemute, a physician and long-time gun-violence researcher at the University of California Davis, said he had contributed more than US$2-million out of his own pocket to fund such work.

“Lots of people left the field and lots of research was never done,” said Dr. Wintemute. “How many thousands of people are dead today who would be alive if the program of research on this major health problem had been left to continue,­ if important questions had been answered, and if prevention programs had been put in place as a result of those answers?”

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Gun-violence researchers often draw parallels between their field and automotive safety. Basic mortality data show that the same number of Americans –­ 36,000 – were killed by guns and by traffic accidents in 2015. But by analyzing the detailed statistics collected in every state on car accidents, researchers have succeeded in identifying ways to make driving safer, whether through learner’s permits, mandatory seat-belt use or changes to the design of vehicles themselves.

Just as no one is suggesting getting rid of cars, “we’re not going to take away everybody’s guns,” said Linda Degutis, the former head of the CDC’s centre for the study of injury prevention. “The point is, how can we make people safe given that there are guns in the environment?”

Earlier this month, the non-profit Rand Corporation published an analysis of the state of research on firearm injuries. It found that the effects of gun policies being discussed by lawmakers “have only rarely – or never – been studied rigorously.” Between 2004 and 2015, the amount the U.S. government spent on gun-violence research was a tiny fraction – 1.6 per cent – of what it spent to study problems with similar levels of mortality, according to a paper published last year.

After the massacre in Newtown, Conn., in 2012, then-president Barack Obama urged Congress to allocate US$10-million to the CDC for research into gun violence. The money was never appropriated. The National Institutes of Health, another major federal research agency, made some grants for gun-violence research starting in 2013, but the program expired early last year and was not renewed.

In recent years, doctors have become more vocal about the need for recurrent funding of such research. Firearm injuries should be studied just like any other type of injury, said Megan Ranney, an emergency physician and professor at Brown University. “I’m not for or against cars, I’m not for or against pools,” she said. “We need the ability to create and gather evidence so that we can do honest, non-partisan, culturally acceptable things so that fewer people die.”

Dr. Ranney is part of the leadership team for a new initiative called the American Foundation for Firearm Injury Reduction in Medicine, which is working to raise funds for such research. Another development is taking place at the state level: Last year, California began distributing a US$5-million grant to support research at the centre run by Dr. Wintemute focusing on gun violence.

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During the state legislature’s debate on the grant, the proposal garnered support from an unexpected source: Jay Dickey. After leaving Congress, the author of the amendment that has squelched gun research for decades had a change of heart. His eponymous measure should be repealed, Mr. Dickey said.