Researchers fr­­om Stanford and Duke University examined recent studies on the causes of gun violence in the United States in an effort to find consensus in a body of research that often covers different states or different time periods, making conclusions difficult to draw.

The analysis by John Donohue, a professor of law at Stanford, and Philip J. Cook at Duke University published Dec. 7 in Science reports some emerging consensus in the studies. Among the findings was that lifting restrictions on concealed carry guns increases violent crime and that laws restricting gun ownership for people convicted of domestic violence reduced killings of female domestic partners.

The authors hope their work can help guide policymakers who are debating measures to reduce gun violence.

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During the crack cocaine epidemic of the late 1980s and the early 1990s, right-to-carry laws were adopted more often in states that had less of a crack problem. This means that any analysis of right-to-carry laws during that period will show those laws as beneficial unless researchers can adequately control for the influence of crack cocaine, which has proved to be quite difficult, Donohue said.

“This problem has plagued every panel data analysis of RTC (right-to-carry) laws, except for those that started after the impact of crack had fully dissipated by the late 1990s and early 2000s,” the researchers wrote.