New Comprehensive National Database Advances Gun Policy Research.

While the number of firearms laws has nearly doubled in the US in the last 26 years, the increase has not been consistent, with some states even decreasing the number of laws, leading to an increasing disparity in the scope of laws potentially impacting violence, according to new research led by the School of Public Health.

In a study published Thursday in the American Journal of Public Health, a team of researchers produced what is considered the most extensive database of state firearms laws in the country, coding 133 different provisions in 14 categories from 1991 to 2016. The provisions cover aspects ranging from regulation of gun dealers, to background checks on private sales, to “stand your ground” laws.

The study found a 57 percent increase in the number of enacted state firearm provisions nationwide from 1991 to 2016 dominated by a handful of states, with 16 states repealing more provisions than they enacted. Over the same time, the national rate of firearm-related homicide decreased from 6.64 per 100,000 population, to 4.13 in 2015.

Lead study author Michael Siegel, professor of community health sciences, said the database is an important step in trying to gauge the impact of laws intended to reduce firearm-related violence. The database aims to allow for “better assessments of the potential impact of state firearm laws on firearm violence. Because we have provided detailed information on a wide range of policies, researchers can now examine the effects of individual and multiple combinations of policies.”

Siegel and co-authors noted that disparities between the numbers of gun laws adopted by states have increased markedly in recent years, and that the adoption of laws has been widely inconsistent. Looking at the impacts of multiple policies over time, they said, allows for “extensive consideration of the potential confounding effects of simultaneously enacted law provisions.”

The authors noted that an increase in the number of enacted firearm laws in a particular state does not necessarily indicate a strengthening of gun laws in that state. States may enact legislation without providing the necessary structures for implementation and enforcement, potentially rendering the laws ineffective.

Alternately, states may choose to focus on a smaller number of laws that they believe are particularly effective at minimizing firearm-related violence.

“It may be more important . . . to consider the effectiveness of individual provisions, rather than considering the aggregate number of laws a state has enacted in a given year,” the authors said.

The study shows a wide disparity in the number of firearm laws enacted across states in the last 26 years, with three states (Alaska, Idaho, and Montana) adopting only 4 of the 133 law provisions, compared to states such as California, Massachusetts, and Connecticut, which enacted at least 89. While California and Connecticut were among states that substantially increased the number of gun law provisions, others sharply reduced the number of those policies.

The study identified five trends in the enactment of state firearm laws intended to protect gun rights, including: the diffusion of “stand your ground” laws, which allow the use of a gun for self-defense without a duty to retreat if people are in a place where they have a right to be; the weakening of concealed-carry permit laws; the adoption of legislation that preempted local governments from enacting their own firearm laws; the enactment of gun industry immunity laws limiting manufacturer liability by preventing potential litigation; and a weakening of state laws that prohibit concealed-carry weapons in schools or on college campuses.

The greatest increases in the number of states that enacted gun laws occurred in areas of laws related to domestic violence; background checks to obtain concealed-carry permits; prohibition of firearm possession by felons; and prohibition of gun possession by people who have been involuntarily committed for inpatient mental health treatment.

The authors said the reporting of the total count of legal provisions in a state should not be interpreted as a “quantitative, linear measure” of the strength of a state’s firearm laws.

“There may be variations in the relative effectiveness of various laws, so any scale that simply sums the total number of law provisions is not necessarily an indication of the public health value of these laws,” they said.

Despite those limitations, Siegel and co-authors said they believe the database will help to advance firearm policy research by allowing more rigorous longitudinal studies.

“Funding deficiencies and political controversy may dissuade researchers, but policy makers need reliable data in order to find ways to mitigate the impact that gun violence has on the lives of thousands of Americans each year,” they said. “Federal and state governments have taken some strides to reduce firearm violence by regulating who can sell and buy firearms, in addition to restricting the conditions under which firearms can be used. We have documented these regulations over time in order to help public health researchers and policy makers determine which of these laws effectively reduce firearm violence, and to what degree.”

The researchers said they hope the database will “spur further efforts to monitor and analyze state firearm law, including efforts that build upon, expand or challenge our work.”

The study is accompanied by a report that includes state-by-state fact sheets and maps with information about trends in state firearm laws. The database itself is available on the project website, along with features that allow users to identify the status of 133 different law provisions in any given state during any of the years from 1991 to 2016.

SPH co-authors include: Molly Pahn, research manager; Ziming Xuan, associate professor of community health sciences; Craig Ross, research assistant professor of epidemiology; and Dean Sandro Galea. Other authors are Bindu Kalesan of the School of Medicine, Eric Fleegler with Children’s Hospital Boston, and Kristin Goss of the Sanford School of Public Policy at Duke University.

Support for the work came from the Robert Wood Johnson Foundation, Evidence for Action Program.

—Lisa Chedekel