The background checks did appear to reduce the rate of gun suicides in men over 55, though the data suggested some men were able to substitute another method when a gun was unavailable.
The findings, reported in 2000 in the Journal of the American Medical Association, reflect a messy truth about most of the measures designed to reduce gun violence: There is little direct evidence they save lives.
Researchers say that does not necessarily mean they are ineffective, just that their impact can be hard to measure in the real world, especially given congressional budget language that discourages federal funding for gun research. Moreover, critics say, some gun-control laws have big loopholes that weaken their impact.
The Obama administration sought to address some of these concerns in the suite of proposals it put forth Wednesday. For example, the requirement for background checks that took effect in 1994, called the Brady Act, applied only to gun sales by licensed dealers. The Obama proposal would expand that to include most private sales.
Likewise, the administration proposed a more comprehensive "assault weapons" ban. A previous ban, which lapsed in 2004, could be circumvented with modifications to prohibited models.
Will these ideas work?
Ironclad proof would require a controlled experiment, wherein some locations were randomly selected for implementation and others were not.
That's unrealistic and potentially dangerous, says Stephen Teret, director of the Johns Hopkins University Center for Law and the Public's Health.
"If you require conclusive proof before you act, then a whole lot more lives are going to be lost," said Teret, who helped advise Vice President Biden's violence task force.
What will happen instead are observational studies, in which researchers try to see whether passage of a law can be statistically linked to any change in the amount of gun violence. That requires taking into account other "confounding" factors that may also play a role, such as income, age, and education.
But reasonable people can disagree on which factors to include and on whether to make certain assumptions about the statistics - such as whether the relationships in question are linear, University of Pennsylvania researcher Charles Branas said.
"There will always be confounders that you couldn't measure that might be affecting the relationship," said Branas, a professor of epidemiology at the Perelman School of Medicine.
It's the sort of mathematical subtlety that can get lost in the public discourse, said Dan Kahan, a professor at Yale Law School who studies risk perception.
People on both sides of the debate cite evidence that is the equivalent of touting Grandma's soup as a cure for the common cold simply because the cold went away a few days after eating it, he said.
"There's something about these issues that turns everyone into some kind of screaming sports fan who is just not going to accept that the player was either in or out of bounds," Kahan said.
A big point of contention in the gun-violence debate is whether having more guns in the hands of law-abiding people serves as a deterrent to criminals.
Hard to say, according to a 2004 review by an expert panel of the National Research Council - the operating arm of the National Academy of Sciences and National Academy of Engineering.
On the contrary, there is evidence that having a firearm in the home is linked to an increased risk of death, including homicides, suicides, and accidents. But in some cases, people might be buying guns because they were in danger to begin with, the panel noted.
Gun owners insist that what is needed is better enforcement of existing laws, and that is true in some cases, said Christopher S. Koper, associate professor of criminology at George Mason University. He helped conduct a survey that found that most law enforcement agencies do not often investigate illegal private sales.
Not all the evidence for gun-violence measures is inconclusive. One that has shown promise is Operation Ceasefire, in which Boston police have worked with other agencies to target specific gangs.
Another is under way in Philadelphia, where the Pennsylvania Horticultural Society has removed trash and planted grass in thousands of vacant lots. Branas, the Penn researcher, led a team that found the greened lots appeared to act as a deterrent for gun crimes when compared with lots that were not cleaned up.
In a paper in the American Journal of Epidemiology, the team proposed several explanations for that phenomenon. Among them: when a lot is cleared of trash and rubble, there is nowhere to hide a gun.
Contact Tom Avril at 215-854-2430 or email@example.com.