In the wake of the shootings in Tucson, Ariz., the familiar questions inevitably resurfaced: Are communities where more people carry guns safer or less safe? Does the availability of high-capacity magazines increase deaths? Do more rigorous background checks make a difference?
The reality is that even these and other basic questions cannot be fully answered, because not enough research has been done. And there is a reason for that: Scientists in the field and former officials with the government agency that used to finance the great bulk of this research agree in saying that the influence of the National Rifle Association has all but choked off money for such work.
"We've been stopped from answering the basic questions," said Mark Rosenberg, former director of the National Center for Injury Control and Prevention, part of the federal Centers for Disease Control and Prevention, which was for about a decade the leading source of financing for firearms research.
Chris Cox, the NRA's chief lobbyist, said his group had not tried to squelch genuine scientific inquiries, just politically slanted ones.
"Our concern is not with legitimate medical science," Mr. Cox said. "Our concern is they were promoting the idea that gun ownership was a disease that needed to be eradicated."
The amount of money available today for studying the impact of firearms is a fraction of what it was in the mid-1990s, and the number of scientists toiling in the field has dwindled to a handful as a result, according to researchers.
The dearth of money can be traced in large measure to a clash between public health scientists and the NRA in the mid-1990s. At the time, Dr. Rosenberg and others at the CDC were becoming increasingly assertive about the importance of studying gun-related injuries and deaths as a public health phenomenon, financing studies that found, for example, having a gun in the house, rather than conferring protection, significantly increased the risk of homicide by a family member or intimate acquaintance.
Alarmed, the NRA and its allies on Capitol Hill fought back. The injury center was guilty of "putting out papers that were really political opinion masquerading as medical science," said Mr. Cox, who also worked on this issue for the NRA more than a decade ago.
Initially, pro-gun lawmakers sought to eliminate the injury center completely, arguing its work was "redundant" and reflected a political agenda. When that failed, they turned to the appropriations process. In 1996, Rep. Jay Dickey, R-Ark., succeeded in pushing through an amendment that stripped $2.6 million from the disease control centers' budget, the very amount it had spent on firearms-related research the year before.
"It's really simple with me," Mr. Dickey, 71 and now retired, said in a telephone interview. "We have the right to bear arms because of the threat of government taking over the freedoms that we have."
The Senate later restored the money but designated it for research on traumatic brain injury.
Language was also inserted into the centers' appropriations bill that remains in place today: "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 prohibition is striking, firearms researchers say, because there are already regulations that bar the use of CDC money for lobbying for or against legislation. No other field of inquiry is singled out in this way.
In the end, researchers said, even though it is murky what exactly is allowed under this provision and what is not, the upshot is clear inside the centers: The agency should tread in this area only at its own peril.
"They had a near-death experience," said Arthur Kellermann, whose study on the risks versus the benefits of having guns in the home became a focal point of attack by the NRA.
In the years since, the CDC has been exceedingly wary of financing research focused on firearms. In its annual requests for proposals, for example, firearms research has been notably absent. Gail Hayes, spokeswoman for the centers, confirmed that since 1996, while the agency had issued requests for proposals that include the study of violence, which may include gun violence, it had not sent out any specifically on firearms.
"For policy to be effective, it needs to be based on evidence," said Garen Wintemute, director of the Violence Prevention Research Program at the University of California, Davis, who had his CDC financing cut in 1996. "The National Rifle Association and its allies in Congress have largely succeeded in choking off the development of evidence upon which that policy could be based."
Private foundations initially stepped into the breach, but their attention tends to wax and wane, researchers said. They are also much more interested in work that leads to immediate results and less willing to finance basic epidemiological research that scientists say is necessary to establishing a foundation of knowledge about the connection between guns and violence, or the lack thereof.
The National Institute of Justice, part of the Justice Department, also used to finance firearms research, researchers said, but that money has also petered out in recent years. (Institute officials said they hoped to reinvigorate financing in this area.)
Stephen Teret, founding director of the Johns Hopkins Center for Gun Policy and Research, estimated that the amount of money available for firearms research was a quarter of what it used to be.
With so much uncertainty about financing, Mr. Teret said, the circle of academics who study the phenomenon has fallen off significantly.
"There are far, far fewer researchers working on the problem," he said. "And, therefore, our knowledge about all aspects of guns and public health has not expanded at the pace that one would hope."