SCOTT DECKER: At the United States Conference of Mayors, March 22, 2007, Scott Decker PhD, School of Criminal Justice and Criminology, Arizona State University, 602-543-8097. Scott.Decker@asu.edu. 

Zero. 5,000. 10,000. 15,000. 20,000. 25,000. 30,000. 35,000. 1975. 1988. 1994. 1996. 1998. 2000. 2002. 2004. Estimated number of gangs based on the reports by city and county law enforcement. 1975-20040 100,000. 200,000. 300,000. 400,000. 500,000. 600,000. 700,000. 800,000. 900,000. 197519881999401996199820002002200 For estimated number of gang members based on reports by city and county law enforcement. 1975-2004. Yes. No. Gang and Nongang Cities Year 2000 National Youth Gang Survey.