(NEW YORK) — This report is a part of “Rethinking Gun Violence,” an ABC News series examining the level of gun violence in the U.S. — and what can be done about it.

Gun violence is an endemic problem in the United States — once again getting worse in some areas after many years of declines and persistent at high levels in others.

Despite being one of the leading causes of death, one thing that’s difficult to know is the scope of the problem, fueled in part by a more than a two-decade-long prohibition — recently changed — on the Centers for Disease Control and Prevention using federal funds to “advocate or promote gun control.”

It wasn’t always this way — the CDC in 1983 adopted a public health approach to gun violence.

“At that point in time in 1983, there were two types of frequent injury deaths. One was motor vehicle crashes, and the other was gun violence,” Dr. Mark Rosenberg, CEO of the Task Force for Global Health and former member of CDC’s National Center for Injury Prevention and Control, told ABC News.

During the 1990s, public and private programs conducted gun-related research — among them was the CDC’s Injury Prevention Program, where Rosenberg worked, and the Violence Prevention Research Program at the University of California, Davis.

But in 1996, Congress passed an amendment to the Omnibus Consolidated Appropriations Bill. The bill modification, commonly known as the Dickey Amendment, prohibited the use of federal funds to “advocate or promote gun control,” leading to the elimination of all CDC funding to conduct firearm-related research — having a lasting impact still limiting what we know today about gun violence.

Even though the funding spigot has recently been turned back on, researchers are still feeling the effects of the lack of data to study gun violence. Researchers say the gun violence problem is urgent and requires an outsized solution detached from politics.

Watch ABC News Live on Mondays at 3 p.m. to hear more about gun violence from experts during roundtable discussions. And check back next week, when we look into what some gun owners say could solve the gun violence issue.

“If we can understand the causes, we can change the effects and we can change the effects for the better, so science is a way to understand the causes and the effects and the way to link them,” Rosenberg told ABC News.

Here’s what to know about the data issue around gun violence and what advocates say can be done:

Impact of the Dickey Amendment

In the early 1990s, the CDC had a $2.6 million budget dedicated to gun violence research both for internal research and for external studies.

“We started looking at, what’s the problem,” Rosenberg told ABC News. The agency studied the number of people dying from gun violence, the weapons used and the causes behind it.

Dr. Garen Wintemute, head of the Violence Prevention Research Program at the University of California, Davis, says the program received two grants at the time to conduct much-needed research on firearms.

“All of these grants made use of unique data that are collected in California,” said Wintemute, who explained to ABC News that the organization was linking gun purchases with criminal records as part of its prevention research.

But everything changed when the Dickey Amendment was introduced by former Rep. Jay Dickey, R-Ark.

Four years before the Dickey Amendment was enacted, the CDC had published its first study on gun violence. The report looked at the correlation between safety and guns, finding that having a weapon in a household didn’t necessarily result in safer outcomes, Rosenberg said.

“These results weren’t pleasing to the NRA. And so they stepped up their attack on our research program,” Rosenberg told ABC News.

ABC News reached out to the National Rifle Association requesting comment on the allegations made by Dr. Rosenberg but has not heard back.

The Dickey Amendment reallocated the $2.6 million away from gun research to other health research on subjects like traumatic brain injury, according to Wintemute.

Researchers fought the effects of the amendment, which prohibited advocacy for gun control — but which had an impact beyond advocacy because experts said they viewed vague language in the amendment as a “threat.”

“This Dickey Amendment had a real chilling effect,” Rosenberg told ABC News. “It was enough to discourage individual researchers and, at the same time, Congress took away the money we were using for the research we were doing.”

The CDC sent ABC News a statement saying it was “subject to appropriations language that states that none of the funds made available to CDC may be used to ‘advocate or promote gun control.”

“The lack of dedicated and sustained research funding for firearm injury… limited our ability to conduct research to gain understanding of how best to prevent firearm-related injuries and deaths relative to other public health problems,” it said.

Shortage of funds

Wintemute’s program suffered from a shortage of federal funds after the amendment passed. Although it was able to continue doing some research through private funding, that work was limited. He originally had around 12 people on his team but says he was left with only four, including himself, limiting the program’s reach.

While The Department of Justice still allocated some funds to firearm research under the National Institute of Justice (the DOJ’s research arm), Wintemute said it was insufficient.

For example, in 2004, a total of $461,759 was granted by the agency to three different institutes for gun-related research — a far cry from the millions normally required for extensive study.

“We had to revert to simpler, more descriptive studies that made use of available data. There wasn’t money to go out and collect data writ large,” Wintemute said.

Other institutions conducting research were also affected.

“Because of the Dickey Amendment, we had dropped firearm injuries from our portfolio,” said Dr. Frederick Rivara, an epidemiologist and professor at the University of Washington, who was conducting research on injury prevention, including firearm-related injuries.

“It really discouraged any serious firearm research,” Rivara said.

This gap in gun research led to a shortage of people familiar with the subject and a lack of data still felt by today’s experts.

“It’ll be another five to 10 years before we have anything like an adequate number of experienced researchers on the case,” Wintemute said.

Research resumes

The need for research and data collection was finally re-addressed by the federal government after the Parkland mass shooting in 2018 that left 17 dead.

After the mass shooting, an omnibus bill was signed by President Donald Trump clarifying that restricting the use of federal funds to advocate or promote gun control doesn’t ban research.

In 2019, Congress began to again allocate funds for research and data collection on gun violence and injuries.

Although the Dickey Amendment remains in place, Dickey, its author who died in 2017, saw the consequences of it on gun-related research and changed his mind, according to Rosenberg — who later became Dickey’s friend.

“Jay Dickey eventually saw the disastrous consequences of gun violence…with mass shootings with rising numbers of gun homicides and gun suicides,” Rosenberg told ABC News. “He switched his position.”

In an op-ed co-authored with Rosenberg in 2012, Dickey says he “served as the NRA’s point person in Congress” to cut the gun violence research budget.

“We were on opposite sides of the heated battle 16 years ago, but we are in strong agreement now that scientific research should be conducted into preventing firearm injuries and that ways to prevent firearm deaths can be found without encroaching on the rights of legitimate gun owners,” reads a section of the piece published in The Washington Post.

More funds needed

Federal funds are now available to study gun violence, but organizations working on policy recommendations are still struggling to conduct it.

“There is more money for research now. But what is missing is datasets,” said Josh Horwitz, executive director of the Educational Fund to Stop Gun Violence, referring to datasets at the federal level that could help in the research on firearms. “We destroy background check records at the federal level in 24 hours… how do you suppose to understand who’s purchasing firearms and what the implications are, if you can’t examine that data,” he added.

The nonprofit, affiliated with the Coalition to Stop Gun Violence located in Washington D.C., focuses on looking for evidence-based policy solutions and programs that can reduce gun-related violence.

“The data deficit has hurt us because we don’t understand all the solutions,” Horwitz told ABC News.

Despite the lack of research, experts say there is still a path forward for finding solutions to the high levels of gun violence plaguing the country.

“This is a solvable problem,” Rosenberg said. “We can find out what are the patterns, what’s the problem, we can find out the causes, we can find out what works to both reduce gun violence and protect gun rights.”

The key to finding possible solutions is focusing on science as opposed to politics, researchers say.

“Science is not advocacy, science is understanding things as they are,” Wintemute said.

While the landscape for gun-related research has improved, there is still a long way to go, Wintemute said.

For fiscal year 2022, Congress approved at least $25 million to fund gun violence research, according to the CDC. And although that represents an increase of $12.5 million compared with the last fiscal year, more resources are needed, according to Wintemude.

“Congress has not followed through,” he said.

He believes the budget for gun-related research has to match the extent of the problem and also help make up for the Dickey Amendment’s toll, including the gaps in data and expertise it created.

“To help get history out of the way and let us attack the problem with a program of research that’s adequate to the size of the problem itself we need to do away with the Dickey Amendment, even as amended,” he added.

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