UCL DEPARTMENT OF SECURITY AND CRIME SCIENCE
Systematic Review of the Empirical Evidence
of Spatial Displacement and Diffusion of
Benefit among Geographically Focused
Policing Initiatives
Dr Shane D Johnson, Dr Kate Bowers, Dr Rob Guerrette,
Lucia Summers and Dr Suzanne Poynton
Department of Security and Crime Science
University College London (UCL)
2010 International NPIA-Cambridge
Conference on Evidence-Based Policing
UCL DEPARTMENT OF SECURITY AND CRIME SCIENCE
Overview
• Background: The need for a review
• Methods:
–
–
–
–
Inclusion criteria
Search strategy
Study coding
Analytic methods
• Results
– Authors’ effect sizes
– Simple proportions
– Meta-analysis
UCL DEPARTMENT OF SECURITY AND CRIME SCIENCE
Background
• Criticisms that focused policing efforts do not address the
“root causes” of crime
• Displacement is the relocation of crime from one place, time,
target, offence, tactic or offender to another as a result of
some crime prevention initiative
• Of the six possible types, spatial displacement is the form
most commonly recognised (Eck 1993)
• At the extreme, widespread displacement stands to
undermine the effects of geographically focused policing
actions
Eck, J.E. (1993). The threat of crime displacement. Criminal Justice Abstracts, 253:527-546.
UCL DEPARTMENT OF SECURITY AND CRIME SCIENCE
Background (cont.)
• Research suggests that crime displacement is rarely total
• At the other end of the displacement continuum is the
phenomenon of diffusion of crime control benefits
• Two (or more) mechanisms for diffusion (Clarke and
Weisburd 1994):
– DETERRENCE: elevated risk of detection and arrest
– DISCOURAGEMENT: effort exceeds anticipated rewards
• Police and others often assume a homogeneous group of
motivated offenders
Clarke, R.V. and Weisburd, D. (1994). Diffusion of crime control benefits: Observations on
the reverse of displacement. In R.V. Clarke (Ed.), Crime Prevention Studies, Vol. 2.
Monsey, NY: Criminal Justice Press.
UCL DEPARTMENT OF SECURITY AND CRIME SCIENCE
The need for a review
• Experiments on the extent of displacement and diffusion
following focused policing efforts, but no systematic
appraisal
• Related reviews:
– Barr and Pease (1990)
– Eck (1993)
– Hesseling (1994)
– Guerette and Bowers
(2009)
Barr, R. and Pease, K. (1990). Crime placement, displacement and deflection. In M. Tonry and
N. Morris (Eds.), Crime and Justice: A review of research, Vol. 12. Chicago: University of
Chicago Press.
Hesseling, R. (1994). Displacement: A review of the empirical literature. In R.V. Clarke (Ed.),
Crime Prevention Studies, Vol. 3. Monsey, NY: Criminal Justice Press.
Guerette, R.T. and Bowers, K. (2009). Assessing the extent of crime displacement and diffusion
of benefits: A review of situational crime prevention evaluations. Criminology, 47(4): 1331-1368.
UCL DEPARTMENT OF SECURITY AND CRIME SCIENCE
METHOD - Paper inclusion criteria
1. Study must evaluate a focused policing intervention
−
−
−
−
−
−
−
hotspot policing/ directed patrol
police crackdown
problem-oriented/ intelligence-led policing project
community policing intervention
broken windows/ Compstat approaches
civil injunctions/ civil remedy
police-led environmental improvement
2. Intervention was ‘geographically focused’ to a local area
− INCLUDED: Census blocks, police
zones/beats/divisions/precincts, estates, districts, suburbs,
block areas, series of roads, neighbourhoods
− EXCLUDED: Very large scale (e.g. entire city)
UCL DEPARTMENT OF SECURITY AND CRIME SCIENCE
METHOD - Paper inclusion criteria (cont.)
3. Quantitative measure of crime
− for the ‘treatment’, ‘control’ and ‘displacement/diffusion
catchment’ areas
− pre- and post-intervention (or pre- and during)
− those without a control area were considered BUT not included
in the meta-analysis
4. Study written in English
5. Paper reported original research findings
– no meta-analyses or reviews
– if multiple papers per study, the most detailed was used
6. Any point in time and any location
7. Both published and unpublished studies
UCL DEPARTMENT OF SECURITY AND CRIME SCIENCE
METHOD – Search strategy
1. Keyword search of electronic abstract databases
(displac* OR “diffusion of benefit” OR “diffusion of benefits” OR “multiplier
effect” OR “free side benefit” OR “ halo effect” OR “spill over*” OR
“free rider effect” OR “bonus effect” OR “spill-over”)
AND
(police OR policing OR law enforcement)
AND
(“hot spot policing” OR ‘hot spots policing” OR crackdown* OR “problem
oriented policing” OR “problem solving” OR “focused policing” OR
“targeted policing” OR “directed patrol” OR “enforcement swamping”
OR “intelligence led policing” OR “broken windows” OR “compstat” OR
“community policing”)
AND
(evaluat* OR impact OR assessment OR test)
UCL DEPARTMENT OF SECURITY AND CRIME SCIENCE
METHOD – Search strategy (cont.)
2. Bibliography search of:
−
−
existing displacement reviews (Barr and Pease 1990; Eck
1993; Hesseling 1994; Guerette and Bowers 2009); and
reviews of the effectiveness of focused policing initiatives
(Braga 2007; Mazerolle et al. 2007; Weisburd et al. 2008).
Braga, A.A. (2007). Effects of Hot Spots Policing on Crime. Campbell Collaboration
systematic review, available from www.campbellcollaboration.org
Mazerolle, L.; Rombouts, S. and Soole, D.W. (2007). Street-level Drug Law Enforcement: A
meta-analytic review. Campbell Collaboration systematic review, available from
www.campbellcollaboration.org
Weisburd, D.; Telep, C.W.; Hinkle, J.C. and Eck, J.E. (2008). The effects of problem-oriented
policing on crime and disorder. Campbell Collaboration systematic review, available from
www.campbellcollaboration.org
UCL DEPARTMENT OF SECURITY AND CRIME SCIENCE
METHOD – Search strategy (cont.)
3. Forward search for works that have cited key displacement
publications (Bowers and Johnson 2003; Clarke 1994;
Clarke and Weisburd 1994; Weisburd et al. 2006)
4. A review of research reports of professional research and
policing organisations
5. Hand search of pertinent journals
Bowers, K. and Johnson, S.D. (2003). Measuring the geographical displacement and diffusion
of benefit effects of crime prevention activity. Journal of Quantitative Criminology, 193:275-301.
Clarke, R.V. (1994). Displacement: An old problem in new perspective. In G. Saville (Ed.),
Crime Problems, Community Solutions: Environmental criminology as a developing prevention
strategy. Port Moody, British Columbia: AAG Inc. Publications.
Weisburd, D.; Wyckoff, L.; Ready, J.; Eck, J.; Hinkle, J.C. and Gajewski, F. (2006). Does crime
just move around the corner? a controlled study of spatial displacement and diffusion of crime
control benefits. Criminology, 443: 549-591.
UCL DEPARTMENT OF SECURITY AND CRIME SCIENCE
Coded studies
Studies coded
Study meets criteria
44
Studies not coded
Paper reports findings presented elsewhere
27
Study meets criteria but cannot source figures
8
Not known if study meets criteria (cannot source
full text / detailed figures no longer available)
8
Study does not meet criteria
202
UCL DEPARTMENT OF SECURITY AND CRIME SCIENCE
Hierarchy of evidence
Data available for
RCT
Quasiexperimental
Treatment
Control
Catchment Catchment
Treatment
Control












N
%
4
9
1
2
2
5

12
27

25
57


Included in meta-analysis
UCL DEPARTMENT OF SECURITY AND CRIME SCIENCE
Analytical strategy
1. Proportional change analysis
2. Summary of effect sizes (ESs) as reported by the study
authors
3. Meta-analysis
4. Weighted Displacement Quotient (WDQ)
[not covered here]
UCL DEPARTMENT OF SECURITY AND CRIME SCIENCE
1.
Proportional
change (N=36)
UCL DEPARTMENT OF SECURITY AND CRIME SCIENCE
2. Summary of authors’ effect sizes
• 19 studies reported statistical test results
• Displacement findings:
– 15: no significant increases in treatment catchment area(s)
– 2: significant increases but intervention not effective
– 2: significant increases for some crime types (1 of 10; 1 of 2)
• Diffusion of benefit findings:
– 8: no significant decreases in treatment catchment area(s)
– 7: significant decreases but only for some crime types, some
of the contiguous areas or when using certain tests AND/OR
when intervention not effective
– 2: significant decreases in treatment catchment area(s)
– 2: inconclusive
UCL DEPARTMENT OF SECURITY AND CRIME SCIENCE
3. Meta-analysis
• Pre- and post-intervention counts of crime commonly
reported
• Sometimes counts not given – BUT in most cases figures
could be converted
• Odds Ratio (OR) calculations used to estimate ES and
CIs for BOTH treatment area and catchment area
(Only possible where numbers are available for a suitable
control area)
• Random effects model used for mean ES
(Many studies have more than one observation for the same
treatment/control/catchment area)
UCL DEPARTMENT OF SECURITY AND CRIME SCIENCE
3.0
Best case scenario (N=15)
Weisburd&Green1995
Treatment
Wagers2007
Catchment
2.5
Sherman&Rogan1995 (Catch 2)
Segrav e&Collins2005 (Dis, Catch 1)
Ratclif f e et al. 2010
MazerollePriceEtAl2000
Higgins&Coldren2000
Grogger2002 (Catchment ctrl)
FarrellEtAl1998 (Pre-Post)
Esbensen1987 (Disorder)
2.0
Increase in Treatment
Decrease in Catchment
Reduction in both areas
Increase in both areas
Reduction in Treatment
1.5
McGarrellEtAl2001
1.0
Catchment Odds Ratio
Press1971(Auto Thef t, Outside)
Cummings2006 (Treatment 1)
0.5
Braga&Bond2008
Braga 1999 (Crime)
Allatt1984 (Pre-Post, Catch 2)
Favors Control
-2
-1
0
0.0
Increase in Catchment
Weighted Mean OR (RDM ef f ects)
Favors Treatment
1
2
Odds Ratio
3
4
5
-2
-1
0
1
2
Treatment Odds Ratio
3
4
UCL DEPARTMENT OF SECURITY AND CRIME SCIENCE
3.0
Worst case scenario (N=14)
Wagers2007
Treatment
Sherman&Rogan1995 (Catch 1)
Catchment
2.5
Segrav e&Collins2005(Prop, Catch 3)
Ratclif f e et al. 2010
Higgins&Coldren2000
Grogger2002 (No catchment ctrl)
FarrellEtAl1998 (Pre-During)
Esbensen1987 (Index Crimes)
Reduction in both areas
Increase in both areas
Reduction in Treatment
1.5
MazerollePriceEtAl2000
Increase in Treatment
Decrease in Catchment
1.0
Catchment Odds Ratio
McGarrellEtAl2001
2.0
Press1971(Burglary , Outside)
Cummings2006 (Treatment 2)
0.5
Braga&Bond2008
Braga 1999 (CFS)
Allatt1984 (Pre-Dur, Catch 1)
Increase in Catchment
Favors Control
-2
-1
0
0.0
Weighted Mean OR (RDM ef f ects)
Favors Treatment
1
2
Odds Ratio
3
4
5
-2
-1
0
1
2
Treatment Odds Ratio
3
4
UCL DEPARTMENT OF SECURITY AND CRIME SCIENCE
200
150
Favors Control
0.7
0.8
0
50
100
1000 MC re-samples
100
50
0
1000 MC re-samples
150
200
Monte Carlo re-samples from all permutations
Favors Treatment
0.9
1.0
1.1
Treatment Mean OR (RDM effects)
1.2
1.3
Favors Control
0.7
0.8
Favors Treatment
0.9
1.0
1.1
Catchment Mean OR (RDM effects)
1.2
1.3
UCL DEPARTMENT OF SECURITY AND CRIME SCIENCE
3.0
RCTs only – best case (N=5)
Weisburd&Green1995
2.5
Treatment
Catchment
Braga&Bond2008
2.0
Reduction in both areas
Increase in both areas
Reduction in Treatment
1.5
MazerollePriceEtAl2000
Increase in Treatment
Decrease in Catchment
1.0
Catchment Odds Ratio
Ratclif f e et al. 2010
0.5
Braga 1999 (Recorded Crime)
Weighted Mean OR (FIXED ef f ects)
Increase in Catchment
-2
-1
0
Favors Treatment
1
2
Odds Ratio
3
4
0.0
Favors Control
5
-2
-1
0
1
2
Treatment Odds Ratio
3
4
UCL DEPARTMENT OF SECURITY AND CRIME SCIENCE
3.0
RCTs only – worst case (N=4)
2.5
Ratclif f e et al. 2010
Treatment
Catchment
2.0
Increase in both areas
Reduction in Treatment
0.5
Braga 1999 (CFS)
Reduction in both areas
1.5
Braga&Bond2008
Increase in Treatment
Decrease in Catchment
1.0
Catchment Odds Ratio
MazerollePriceEtAl2000
Weighted Mean OR (RDM ef f ects)
Increase in Catchment
Favors Treatment
0.0
Favors Control
-2
-1
0
1
2
Odds Ratio
3
4
5
-2
-1
0
1
2
Treatment Odds Ratio
3
4
UCL DEPARTMENT OF SECURITY AND CRIME SCIENCE
Conclusions
Results suggest that, on average, geographically focused
policing initiatives for which data were available were:
• associated with significant reductions in crime and disorder
• overall, changes in (immediate) catchment areas are nonsignificant but there is a trend in favour of a diffusion of benefit
• for RCTs, there is a diffusion of benefit and the mean effect is
statistically significant
More in the review:
• WDQ analysis
• Differences by intervention type, size of treatment area, etc.
• Discussion of methodological issues
UCL DEPARTMENT OF SECURITY AND CRIME SCIENCE
Thank you for your attention
Lucia Summers
l.summers@ucl.ac.uk
2010 International NPIA-Cambridge
Conference on Evidence-Based Policing