We examined the gang problems of the four study sites by analyzing official police gang data collected by the police departments. In particular, we focus on recent trends in the numbers of gangs, gang members, and gang crimes in each city. This data serves as a common reference point to which we can observe the current or objective gang problem. When we refer to the “current” or “objective” gang problem in each city, our understanding of that is based on and limited by information provided to us. Although we attempted to gather official police data from each department dating back ten years or more for an examination of recent trends in gangs, gang members, and gang crime, many agencies had not collected this data or had not retained it. Some of the agencies were able to provide information for all ten years, but others were able to provide only one year's worth of data, and still others could provide official data only on some issues and for intermittent periods.

We also augment the official data with interview data obtained from gang unit officers as well as each unit's internal and external stakeholders.