Oct. 20 (UPI) — More permissive concealed carry laws — those that grant greater access to concealed firearms — are associated with increased homicide rates, according to new research.

Researchers at the Boston University School of Public Health analyzed the relationship between changes in gun laws and the firearm-related homicide rates in all 50 states between 1991 and 2015.

Concealed firearm permits are issued in all 50 states, but some state laws provide local police with a greater amount of discretion in deciding whether to issue someone a license.

“May issue” laws are on the books in nine states; in these states, law enforcement officials can decline to issue a concealed carry license to anyone they deem to be at risk of committing violence, whether or not they have a criminal history.

Researchers categorized the concealed carry laws of 29 states as “shall issue.” In these 29 states, police are given little to no discretion. In 12 states, concealed firearms can be carried without a permit.

In analyzing the trends in local gun violence, researchers found a link in the passage of more lenient concealed carry laws and rises in homicide rates.

Data from the Federal Bureau of Investigation’s Uniform Crime Reports Supplementary Homicide Reports helped researchers differentiate between homicides involving hand guns — those regulated by concealed carry laws — and long-barreled guns. Previous gun studies have failed to account for the distinction, researchers explained.

The analysis — detailed in the American Journal of Public Health — revealed a 10.6 percent higher handgun homicide rate in “may issue” states than “shall issue” states.

“Some have argued that the more armed citizens there are, the lower the firearm homicide rate will be, because the feared or actual presence of armed citizens may deter violent crime,” Michael Siegel, professor of community health sciences at BUSPH, said in a news release. “Our study findings suggest that this is not the case.”

While a handful of studies have found links between gun ownership and decreases in violent crime, the majority of studies have found the opposite.

Congress is currently considering whether to grant nationwide reciprocity to concealed carry permit holders. That means all states would have to honor a concealed carry permit granted in a person’s state of residence. Public health officials and gun safety advocates have raised concerns that such a law would make Americans less safe.

“The trend toward increasingly permissive concealed carry laws is inconsistent with public opinion, which tends to oppose the carrying of guns in public,” authors wrote in their new study. “Our findings suggest that these laws may also be inconsistent with the promotion of public safety.”