Legislation at the federal, state, and local levels has attempted to address gun violence through a variety of methods, including restricting firearms purchases by youths and other "at-risk" populations, setting waiting periods for firearm purchases, establishing gun buyback programs, law enforcement and policing strategies, stiff sentencing of gun law violators, education programs for parents and children, and community-outreach programs. Despite widespread concern about the impacts of gun violence on public health, Congress has prohibited the Centers for Disease Control (CDC) from conducting research that advocates in favor of gun control.[19] The CDC has interpreted this ban to extend to all research on gun violence prevention, and so has not funded any research on this subject since 1996.[20]