Guns seized by the New York Police Department in the largest seizure of illegal guns in the city's history, announced this summer. 2013 Getty Images

A new study published in the American Journal of Public Health on Thursday has found a “robust” relationship between rates of gun ownership and firearm homicide, challenging the National Rifle Association’s assertion that more registered guns equal fewer firearm-related deaths.

However, the study noted that while gun ownership is a significant predictor of firearm homicide rates, the correlation did not necessarily mean that higher ownership directly caused more gun-related killings.

The researchers looked at firearm homicide data in all 50 states between 1981 and 2010 and found that for each 1 percent increase in gun ownership, a state's firearm homicide rate jumped by 0.9 percent.

Led by Boston University School of Public Health researcher Michael Siegel, the study says it is “the most up-to-date and comprehensive analysis of the relationship between firearm ownership and gun-related homicide rates among the 50 states.”

"We observed a robust correlation between higher levels of gun ownership and higher firearm homicide rates," the study said.



The lowest firearm homicide rate was found to be in New Hampshire, at 0.9 per 100,000 people; Louisiana registered the highest, with a rate of 10.8 per 100,000.

The Boston University model predicts that “if the gun ownership estimate for Mississippi were 58 percent (the average for all states), instead of 77 percent (the highest of all states), its firearm homicide rate would be 17 percent lower.”

Because no data was available on gun ownership rates for some states, Siegel’s team relied on a proxy measure: firearm suicides divided by all suicides, or FS/S. Researchers say the FS/S proxy is well established and reliable.

Notably, the Boston University study was not able to determine a causal relationship between gun ownership and firearm homicide rate, leaving open the possibility of an alternate explanation: that residents of states where firearm homicides are on the rise might be flocking to gun depots for protection.

"Although we could not determine causation, we found that states with higher levels of gun ownership had disproportionately large numbers of deaths from firearm-related homicides," the researchers wrote.

Neither the NRA nor the gun rights advocacy group Gun Owners of America immediately commented on the study.

The introduction to the Boston University study mentions the Dec. 12, 2012, shooting at Sandy Hook Elementary School in Newtown, Conn., which left 26 dead, including 20 children, as an inspiration for further research on the connection between gun proliferation and homicide.

In the wake of the Sandy Hook killings, divergent narratives emerged about how such tragedies can be prevented. While the incident spurred President Barack Obama to push for a ban on assault weapons like the one the shooter used at Sandy Hook, gun rights advocates offered a different solution.

In a news conference a week after Sandy Hook, NRA executive vice president Wayne LaPierre suggested that armed police officers be stationed outside every American school, saying that “the only thing that stops a bad guy with a gun is a good guy with a gun.”

Reuters news agency reported in January that hundreds of teachers in Ohio and Texas had signed up for discounted or free arms training in those states in reaction to Sandy Hook.

As the Obama administration advocates stricter regulation, including universal background checks for anyone purchasing a gun, the United States is experiencing a movement among states to nullify federal laws on gun control that local legislators reject. New York and Connecticut have already broken with federal standards and enacted stricter laws.

The Boston University study comes during a busy week for gun-related legislation. A Missouri measure attempting to nullify some federal gun control laws fell a single vote short of enactment Wednesday in one of the boldest examples of this trend.

In other gun control news, sheriffs in Iowa are granting blind and visually impaired residents gun permits, the Des Moines Register reported Sunday.

Jane Hudson, executive director of Disability Rights Iowa, said keeping legally blind people from obtaining weapon permits would violate the Americans With Disabilities Act.

With wire services