High rates of gun mortality and injury are often cited as a primary impetus for gun control policies.[23] A 2004 National Research Council critical review found that while some strong conclusions are warranted from current research, the state of our knowledge is generally poor.[24] The result of the scarcity of relevant data is that gun control is one of the most fraught topics in American politics[25] and scholars remain deadlocked on a variety of issues.[25] Notably, since 1996, when the Dickey Amendment was first inserted into the federal spending bill, the United States Centers for Disease Control and Prevention has been prohibited from using its federal funding "to advocate or promote gun control," thwarting gun violence research at the agency at the time. The funding provision's author has said that this was an over-interpretation,[26] but the amendment still had a chilling effect, effectively halting federally funded firearm-related research.[27] Since the amendment, the CDC has continued to research gun violence and publish studies about it,[28] although their funding for such research has fallen by 96% since 1996, according to Mayors Against Illegal Guns.[29] According to a spokesman, the CDC has limited funding and has not produced any comprehensive study aimed at reducing gun violence since 2001.[30]