Diffusion in Homicide: Exploring a General Method for Detecting Spatial Diffusion Processes

This article proposes a new method for examining dynamic changes in thespatial distribution of a phenomenon. Recently introduced exploratoryspatial data analysis (ESDA) techniques provide social scientists with anew set of tools for distinguishing between random and nonrandom spatialpatterns of events (Anselin, 1998). Existing ESDA measures, however, arestatic and do not permit comparisons of distributions of events in the samespace but across different time periods. One ESDA method—the Moranscatterplot—has special heuristic value because it visually displayslocal spatial relationships between each spatial unit and its neighbors. Weextend this static cross-sectional view of the spatial distribution ofevents to consider dynamic features of changes over time in spatialdependencies. The method distinguishes between contagious diffusion betweenadjoining units and hierarchical diffusion that spreads broadly throughcommonly shared influences. We apply the method to homicide data, lookingfor evidence of spatial diffusion of youth-gang homicides acrossneighborhoods in a city. Contagious diffusion between neighboring censustracts is evident only during the year of peak growth in total homicides,when high local rates of youth-gang homicides are followed by significantincreases in neighboring youth- nongang rates. This pattern is consistentwith a spread of homicides from gang youth to nongang youth. Otherwise, theincreases in both youth-gang and youth- nongang homicides generally occursimultaneously in nonneighboring tracts.     

Oil, Arms, and Influence: The Indirect Strategy Behind Chinese Military Modernization

According to a recent RAND report, the United States will not be able to defend Taiwan from Chinese military aggression by 2020. However, this study, like many others, raises more questions than it answers about the People's Republic of China's (PRC's) current defense posture.¹ Is there a Chinese plan to claim Taiwan by force after 2020? In contrast to the conclusions of the RAND report, this article argues that China's strategic approach is not designed primarily for fighting a war over Taiwan, or over any other matter of critical interest to China, but to create a disposition of forces so favorable to Beijing that China will not need to fight a war. Rather than thinking of China's strategy as a blueprint for using military power to secure territory or vital resources, such as oil, it may be more appropriate to consider the possibility that Beijing's actions are directed at obviating the need to fight. Beijing may calculate that it can render its interests unassailable by constructing a network of friendly or dependent states by means of arms transfers and the like. The basis of such a strategy is the assumption that China's prospective enemies, finding themselves encircled or obstructed by powers aligned with Beijing, will be unable to envision a military campaign to deny China oil at an acceptable level of costs. They will, therefore, be deterred from threatening China, e.g. by interrupting its oil supplies. It is a mark of the efficacy of this broader deterrence strategy that American security analysts are already ruling out a successful defense of Taiwan in 2020. Similarly, the early stages of an effort to insulate China from an energy-related challenge are already visible.