Throughout the cleaning and analysis of the data, differences emerged regarding the validity of each data source and their meaningfulness in analysis, common concerns that have been well documented (Decker, 1978; Klinger and Bridges, 1997; Sherman, Gartin,and Buerger, 1989).
These differences presented problems at all stages of this research,including selecting, cleaning, and analyzing spatially referenced data (see Lum, 2003, for a detailed discussion of this problem in Seattle).
In short, it became clear that written report data under reported drug activity, arrest data under reported violent crime, and dispatcher coded 911 calls systematically miscoded call types and their locations for a variety of reasons (for example, there were no records of homicide in the dispatcher database and addresses were often not specified).