Spatial displacement and diffusion of benefits among geographically-focused policing initiatives

Additional Info

  • Authors: Kate Bowers, Shane Johnson, Rob Guerette, Lucia Summers, Suzanne Poynton
  • Published date: 2011-06-15
  • Coordinating group(s): Crime and Justice
  • Type of document: Title, Protocol, Review, User abstract
  • Volume: 7
  • Issue nr: 3
  • Category Image: Category Image
  • Title: Spatial displacement and diffusion of benefits among geographically-focused policing initiatives
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Background

One of the most common criticisms of spatially focused policing efforts (such as Problem-Oriented Policing, police ‘crackdowns’ or hotspots policing) is that crime will simply relocate to other times and places since the “root causes” of crime were not addressed. This phenomenon—called crime displacement—has important implications for many policing projects. By far, spatial displacement (movement of crime from a treatment area to an area nearby) is the form most commonly recognized. At the extreme, widespread displacement stands to undermine the effects of geographically focused policing actions. More often, however, research suggests that crime displacement is rarely total. On the other end of the displacement continuum is the phenomenon of ‘diffusion of crime control benefits’ (a term coined by Ron Clarke and David Weisburd in 1994). Diffusion occurs when reductions of crime (or other improvements) are achieved in areas that are close to crime prevention interventions, even though those areas were not actually targeted by the intervention itself.

Objectives

To synthesize the evidence concerning the degree to which geographically focused policing initiatives are related to spatial displacement of crime or diffusion of the crime control benefits.

Search strategy

A number of search strategies were used to retrieve relevant studies. First, we undertook a keyword search of electronic abstract databases. Second, we searched bibliographies of existing displacement reviews and reviews of the effectiveness of focused policing initiatives. Third, we did forward searches for works that had cited key displacement publications. Fourth, we reviewed research reports of professional research and policing organizations. Fifth, we undertook a hand search of pertinent journals and publications. Finally, once these searches were all completed we emailed a list of the studies that we had assessed as meeting (and a separate list of those not meeting) our criteria to a number of key scholars with knowledge of the area to identify any further studies we might have missed.

Selection criteria

Eligible studies met the following criteria; (1) they evaluated a policing initiative; (2) this initiative was geographically focused to a local area; (3) the evaluation included a quantitative measure of crime for both a ‘treatment’ area and a displacement/diffusion ‘catchment’ area. This needed to be available for both a pre- and a post- (or during-) intervention period. Other criteria specified that the study was written in English and that it reported original research findings. The studies could have been conducted at any point in time and at any location. Both published and unpublished studies were included.

Data collection and analysis

For all of our 44 eligible studies, we produced a narrative review and a summary of the author’s findings, concerning the effectiveness of the policing initiative and any displacement or diffusion observed. For the 16 studies for which we were able to gain pre and post measures of crime for each of a minimum of three area types (a treatment, control and catchment area) we produced odds ratio effect sizes which were used in a meta-analysis. For the meta-analysis we reported the mean effect size for both the treatment areas and the catchment areas. This summarized the effectiveness of the policing interventions and the displacement/diffusion effect respectively. Because a number of studies had more than one primary outcome, we reported the largest effect and the smallest effect in each case. We also performed permutation tests using combinations in which one primary outcome was chosen from each study. Other tests assessed the effects of study design, intervention type, size of intervention and publication bias. A further quantitative analysis of these 16 studies summarised the mean Weighted Displacement Quotient (WDQ) a measure developed in earlier work by two of the study authors. Finally, a proportional change analysis looked at increases and decreases in crime in treatment and catchment areas for the 36 studies for which count data were available. This analysis did not require data to be available for a control area.

Main results

The main findings of the meta-analysis suggested that on average geographically focused policing initiatives for which data were available were (1) associated with significant reductions in crime and disorder and that (2) overall, changes in catchment areas were non-significant but there was a trend in favour of a diffusion of benefit.

For the weighted displacement quotient analyses, the weight of the evidence suggests that where changes are observed in catchment areas that exceed those that might be expected in the absence of intervention, a diffusion of crime control benefit rather than displacement appears to be the more likely outcome.

The results of the proportional change analysis suggest that the majority of eligible studies experienced a decrease in crime in the treatment area indicating possible success of the scheme. The majority also experience a decrease in the catchment areas suggesting the possibility of a diffusion of benefit. These findings, which could not be statistically tested, are consistent with all others reported here, and with those from the narrative review.

Conclusions

In summary the message from this review is a positive one to those involved in the sort of operational policing initiatives considered, the main point being that displacement is far from inevitable as a result of such endeavor, and, in fact that the opposite, a diffusion of crime control benefits appears to be the more likely consequence.

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