Restricting exactly who has access to guns may be the most effective way to curb firearm deaths in America – even more so than limiting the types of guns available or when they may be used, according to new research published in the Journal of General Internal Medicine .

From 1997 to 2016, the U.S. saw an annual average of 3.5 gun homicides per 100,000 people, researchers say, with rates ranging from 0.7 in New Hampshire to 9.8 in Louisiana . States that had enacted two types of measures that can limit certain people's access to firearms during a slightly broader time period assessed for the published study – 1991 to 2016 – had lower gun homicide rates, while policies banning guns themselves appear to have done little to curb the death rates.

"Laws that are really focused on making sure the highest-risk individuals cannot access guns … seem to really have the greatest impact," says Dr. Michael Siegel, the study's lead author and a professor of community health sciences at the Boston University School of Public Health . "The single greatest risk factor for violence is a history of violence."

Across U.S. states, laws banning gun possession for people who had been convicted of a violent misdemeanor were associated with an 18.1 percent reduction in gun homicide rates, Siegel's study found, while universal background checks were linked to a 14.9 percent decline. For the study, just five states as of 2016 met researchers' criteria for restricting gun possession for people with a violent misdemeanor conviction, while 12 states required universal background checks for firearm sales. ( North Dakota , Vermont and Wyoming were excluded from the homicide analysis because of insufficient data.)

Meanwhile, states with "shall issue" laws – which generally require law enforcement to issue a concealed carry permit to anyone who meets minimal requirements – were associated with a 9 percent increase in gun homicide rates. Seven types of gun control laws, including bans on the sale of assault weapons and high-capacity magazines, were not significantly linked to either an increase or decrease in gun homicide rates.

"Laws that regulate the 'what' – the types of weapons that are available – seem to have very little impact on overall homicide rates," Siegel says. "But laws that regulate the 'who' – who may have access to weapons – appear to have a really substantial impact."

While Siegel acknowledges that states with lower homicide rates in the first place also may be more likely to enact stronger gun laws, researchers took three steps to mitigate bias in the results: They evaluated homicide rates the year after a state passed a new law, measured gun homicide rates against overall homicide rates, and looked at gun laws and homicide rates over a quarter of a century.

During the time period studied, there were a total of 93 changes to state gun laws, with 22 states enacting "shall issue" laws and 24 states implementing "stand your ground" laws, which allow the use of deadly force for self-defense.

There were just a relative handful of law changes dealing with who may buy or own a gun during that time frame, though federal and state lawmakers are now considering such measures. In February, the U.S. House of Representatives passed a bill that would require universal background checks for firearm purchases, though it may stumble in the Republican-controlled Senate.

"For pure political feasibility, it seems unlikely that Congress, at the current time, will do this," Siegel says of any proposed federal gun control legislation. "We think the action's going to happen at the state level."

Last week, the gun control nonprofit Everytown for Gun Safety introduced a campaign to educate people about so-called red flag laws, which can allow judges to restrict gun access for people who may pose a danger to themselves or others, The Washington Post reported.

North Carolina legislators are considering a red flag law, and The Associated Press reported in February that nine states had enacted such a measure since last year's mass shooting in Parkland, Florida , bringing the total number of states with red flag laws to 14.

The Senate Judiciary Committee also held a hearing on state red flag laws Tuesday, during which committee chair Sen. Lindsey Graham, R-S.C., said it was unlikely a federal red flag law would pass, but that he would encourage ways for states to enact their own measures.