Recent mass shootings have revived demands for meaningful gun control. But many opponents of a renewed federal ban on assault weapons, led by the National Rifle Association, say the earlier ban, from 1994 to 2004, made no difference. Our new research shows otherwise.

We found that public mass shootings leading to at least six deaths dropped during the decade of the federal ban, with fatalities falling by 40 percent. In the 15 years since the ban ended, the trajectory of gun massacres has been sharply upward, largely tracking with the growth in ownership of military-style weapons and high-capacity magazines.

Using the Mother Jones mass shooting database, we identified the number of gun massacres — which we defined as incidents in which a shooter killed at least six people in public — over a 35-year period. (We also followed the F.B.I.’s approach of excluding crimes of armed robbery and gang or domestic violence in evaluating public active shooter incidents.) Compared with the decade before its adoption, the federal assault weapon ban in effect from September 1994 through 2004 was associated with a 25 percent drop in gun massacres (from eight to six) and a 40 percent drop in fatalities (from 81 to 49).