Federal funding for research on leading causes of death Cancer H.I.V. Diabetes Heart disease Lung disease $10 billion in Federal funding Alzheimer’s disease Cerebrovascular disease Hypertension Atherosclerosis Parkinson’s disease Sepsis Malnutrition Viral hepatitis Aspiration Influenza and pneumonia $1 billion Fires Poisoning Nephritis, nephrotic syndrome, and nephrosis Biliary tract disease Intestinal infection Motor vehicles Asphyxia Peptic ulcer $100 million Penetrating wounds Hernia Gun violence Drowning $10 million Falls 1 death per 100,000 people 10 50 100 150 200 Cancer H.I.V. Diabetes Heart disease $10 billion Hypertension Atherosclerosis Parkinson’s disease Malnutrition Viral hepatitis Influenza and pneumonia $1 billion Poisoning Fires Intestinal infection Motor vehicles Asphyxia Peptic ulcer $100 million Hernia Gun violence Drowning $10 million Falls 1 death per 100k people 10 50 100 150 Cancer H.I.V. Heart disease Diabetes $10 billion Hypertension Malnutrition $1 billion Fires Poisoning Motor vehicles Asphyxia $100 million Gun violence Drowning $10 million 1 death per 100k people Falls 10 50 100 Source: From 2004 to 2014, David Stark and Nigam Shah, Funding and Publication of Research on Gun Violence and Other Leading Causes of Death

It's a measure of the divisiveness of guns in the United States that federal public health officials barely spend any money funding gun violence research.

Because of the deaths of students and teachers in Parkland, Fla., last month, there's a chance this will change.

When someone dies in a car crash, the local police fill out a detailed form that is shared with the federal government. Researchers have mined that data to see how policies — in road design, licensing rules, seatbelt laws or car requirements — can reduce the death toll from driving.

When someone is killed in a shooting, the data collected is skimpier, more haphazard and not reported to the federal government from every state. That lack of information isn’t the main reason gun policy remains such a political and controversial issue in American life. But it does limit the ability of policymakers to fully understand what laws could make a difference.

Over all, the federal government spends far, far less on research into gun violence than it does on other health risks that kill a comparable number of Americans each year. As a result, gun deaths are the subject of substantially less scholarship.

But after decades of meager funding from federal officials, Alex Azar, the secretary of health and human services, testified in February that the department should invest in gun violence research — and his priorities could shape the spending agenda. The possible repeal of legislative language barring certain officials from using money to “advocate or promote gun control” came up several times during this week’s roundtable discussion between President Trump and members of Congress on possible new gun legislation.

Scholars at the nonpartisan RAND corporation recently surveyed the current evidence about gun safety and violence. After a two-year study, they published their results Friday, with a big review of the literature and a set of research recommendations. One of their biggest conclusions was that we don’t have very good evidence on many gun safety questions at all. “There has been fairly little research compared to other causes of mortality,” said Andrew Morral, a senior behavioral scientist at RAND, who was the lead author on the survey. “A lot of the research that has been done has been fairly ambiguous, so both sides can pick it apart fairly easily.”

The RAND team went through all the published research on the effects of gun policies and found relatively few studies that it found persuasive. It took those studies and plotted them on a table of major questions the country might want to know about gun violence prevention. Lots of areas remain unstudied.

If government support for research opened up, what should researchers study? We asked 29 experts on guns — trained in criminology, economics and public health — for their proposed research priorities. Eighteen responded, sharing a range of suggestions about the most important unanswered questions about guns that they’d like to see explored.

According to RAND, here’s a look at the evidence that these policies reduce various harms or increase them (in the case of stand-your-ground and concealed-carry laws): Blank cells mean that no studies met RAND’s criteria. Unclear means that included studies found only uncertain or suggestive effects. Limited means that at least one study suggested an effect. Moderate means that two or more studies suggested similar effects. Strong means that three found the same effects using at least two independent data sets. The green cells for stand-your-ground and concealed-carry laws represent increases; all others represent reductions. More policies and effects are available at Gun Policy in America

What are the most important questions?

Six of our experts were most interested in where the guns used in shootings came from. While the federal government collects records about the sales of new guns from federally licensed gun dealers, there is far less information about what happens to guns after they leave the store. Several of our experts said more detailed tracking of where guns go and how they reach the hands of criminals through secondary and black markets could significantly improve our understanding of what policies might reduce violence and injuries.

In the 1980s, a major survey of felons uncovered patterns in how they obtained and used guns. Since then, there has been no comparable large study. “Because we lack any sort of systematic data across (and within) states, it's impossible to know how guns move through population,” wrote Andrew Papachristos, a sociologist at Northwestern University.

Five of our panelists said the most important question was not about guns at all, but about the factors that lead individuals into violence, and what could prevent it. “We need to know more about the effective treatments for those involved in violence — to change their behavior and risk level,” wrote Charlie Ransford, the senior director of science and policy for the nonprofit group Cure Violence.

Some suggestions were more idiosyncratic. Liza H. Gold, a psychiatrist at Georgetown University, said she’d like to know more about the effects of gun violence restraining orders, which allow a judge to order the temporary confiscation of guns from a person ruled to be dangerous. Matthew Miller, a public health scholar at Northeastern University, said there’s more to understand about why people decline to unload and lock guns in storage, particularly when children are nearby. Adam Lankford, a criminologist at the University of Alabama, said we need more research into how more restrictive gun laws affect the lives of law-abiding gun owners.

What key information are we missing?

The lack of direct government funding is one of the reasons these questions remain unanswered, but our panelists also said one of the main obstacles to meaningful research was a lack of detailed national data of the sort the federal government is uniquely able to demand and collect.

We asked them to name the data set they can’t access now but most want to study.

Several requested a detailed record of the circumstances around every shooting, including murders, suicides, accidental deaths — something akin to the data collected on highway crashes. A few said that information about nonfatal shootings, rarely collected, could also be useful.

Several researchers longed for basic information about how many guns are in circulation and who owns them. “Who owns and how many assault weapons are there in the U.S.?” said Robert Spitzer, a political scientist at SUNY Cortland, one of several researchers who wished for an inventory of American guns.

“How many weapons are sold, what kind, where?” suggested Magdalena Cerdá, an epidemiologist at the University of California at Davis.

Stephen Teret, a public health scholar at Johns Hopkins, started his career studying traffic fatalities, before shifting to gun deaths. He recounted how the granular details in the car crash data enabled researchers to recognize that rollover crashes were particularly likely in vehicles with design features that caused them to have a higher center of gravity.

The data showed them the risks of beautification campaigns that encouraged trees to be planted near highways. It showed that teenage drivers with teenage passengers were more likely to crash. Those findings led to changes in policy, and the traffic fatality rate has declined over decades.

Traffic safety data was collected after public outcry about the deadliness of cars led to the creation of a government agency to study the subject. “That’s a remarkable success story for public health,” he said. “We didn’t see the same reduction in firearm-related deaths.”