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Spatially Integrated Social Science: Chapter 9
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Measuring Spatial Diffusion of Shots Fired Activity Across City Neighborhoods
George Tita and Jacqueline Cohen
Abstract
Social scientists interested in crime often ask one of two questions: "Why does the distribution of crime differ over place?" or "Why does the level of crime within a place change over time?" Examining these questions separately, however, ignores a potentially richer understanding arising from space/time interactions in crime. This chapter extends earlier work by Cohen and Tita (1999) on a general method for identifying changes in spatial and temporal patterns of homicide that are compatible with various forms of diffusion. Building on Anselin's work on "local indicators of spatial association" (LISA statistics), the method explores the dynamics of changes over time in patterns of spatial concentration in homicide across neighborhoods within a city. The method distinguishes between contagious diffusion between adjoining units and hierarchical diffusion that spreads broadly through commonly shared influences. The current analysis examines patterns of spatial diffusion in non-lethal precursors to gun violence reflected in calls to police reporting "shots fired" incidents.
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