Shane D. Johnson

Measuring the Geographical Displacement and Diffusion of Benefit Effects of Crime Prevention Activity

The displacement of crime is an important criminological phenomenon. However, while there has been theoretical discussion of this issue in the research literature, there has been little in the way of either standardized empirical work that investigates the incidence of displacement or in the development of techniques that can be used to measure it. In the current paper we discuss a new technique, the weighted displacement quotient (WDQ), that was developed to measure the geographical displacement of crime. A critical feature of the rationale is that displacement can only be attributed to crime prevention activity if crime is reduced in the target area considered. Thus, the WDQ not only measures what occurs in a buffer (displacement) zone but also relates changes in this area to those in the target area. Part of the appeal of the measure is that it can be used either with aggregate or disaggregate crime data and for any geographical boundary selected, provided the appropriate data are available. In addition to detecting displacement, when detailed data are available, the technique can also be used to identify where the effect was most prominent. The WDQ can equally be used to measure the diffusion of benefit of any crime prevention activity. A series of examples are presented for illustration purposes.

Crime mapping as a tool for security and crime prevention.

There is no doubt that crime mapping is now a mainstream practice in police organizations and the security industry more generally (Wartell and McEwen, 2001). For example, a Home Office survey (Weir and Bangs, 2007) conducted in 2005, with responses from 35 of the 43 UK police forces and many of the UK Crime and Disorder Reduction Partnerships (CDRPs), revealed that 90% of the 171 respondents used Geographic Information Systems (GIS), with three-quarters using them at least weekly. In terms of training, most respondents assessed themselves as competent or proficient users. Commonly used methods included point mapping of individual incidents of crime (86%) and the thematic mapping of data to boundaries such as local authority wards or police beats (80%). Only 50% of respondents used hotspot mapping and where used kernel density estimation (a smoothed risk surface over which crime risk is interpolated from a point pattern) and grid thematic mapping were employed. Of practical concern, when asked how the mapping they undertook informed operational decisions, only 29% felt that it was always or frequently used, with 25% stating that their analyses were very infrequently or never used.

Poetry in motion: The case of insider and outsider offenders

Marcus Felson is not only an exceptional scholar, a great colleague, and a good friend, but he is also a man who is very free with his ideas. This chapter focuses on just one of the many ideas that Marcus has given us over the years that we have known him. We picked this idea in particular because it fuses together two of the subjects that we know are dear to his heart. The first subject, which we are sure will be mentioned on numerous occasions throughout this book, is guardianship. The second is how temporal patterns of crime can reveal clues as to the possible causes of crime or their prevention.