Research by gun advocate John Lott found no impact of these bans on violent crime rates,[36] but provided evidence that the bans may have reduced the number of gun shows by over 20 percent.[37] Koper, Woods, and Roth studies focus on gun murders, while Lott's look at murder, rape, robbery, and aggravated assaults. Unlike their work, Lott's research accounted for state assault weapon bans and 12 other different types of gun control laws.