ucl department of security and crime science systematic review of the empirical evidence of spatial...

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


Overview

• Background: The need for a review

• Methods:– Inclusion criteria

– Search strategy

– Study coding

– Analytic methods

• Results– Authors’ effect sizes

– Simple proportions

– Meta-analysis


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.


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.


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)

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.

– Guerette and Bowers (2009)


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)


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


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)


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


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.


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


Hierarchy of evidence

Data available for

Treatment ControlTreatment Catchment

Control Catchment

N %

RCT 4 9

1 2

Quasi-experimental

2 5

12 27

25 57

Included in meta-analysis


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]


1. Proportional

change (N=36)


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


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)


Best case scenario (N=15)

Odds Ratio

Weighted Mean OR (RDM ef f ects)

Allatt1984 (Pre-Post, Catch 2)

Braga 1999 (Crime)

Braga&Bond2008

Cummings2006 (Treatment 1)

Esbensen1987 (Disorder)

FarrellEtAl1998 (Pre-Post)

Grogger2002 (Catchment ctrl)

Higgins&Coldren2000

MazerollePriceEtAl2000

McGarrellEtAl2001

Press1971(Auto Thef t, Outside)

Ratclif f e et al. 2010

Segrav e&Collins2005 (Dis, Catch 1)

Sherman&Rogan1995 (Catch 2)

Wagers2007

Weisburd&Green1995

-2 -1 0 1 2 3 4 5

Treatment

Catchment

Favors TreatmentFavors Control

-2 -1 0 1 2 3 4

0.0

0.5

1.0

1.5

2.0

2.5

3.0

Treatment Odds Ratio

Cat

chm

ent O

dds

Rat

io

Reduction in both areas

Reduction in Treatment

Increase in Catchment

Increase in Treatment

Decrease in Catchment

Increase in both areas


Worst case scenario (N=14)

Odds Ratio


Allatt1984 (Pre-Dur, Catch 1)

Braga 1999 (CFS)

Braga&Bond2008

Cummings2006 (Treatment 2)

Esbensen1987 (Index Crimes)

FarrellEtAl1998 (Pre-During)

Grogger2002 (No catchment ctrl)

Higgins&Coldren2000


McGarrellEtAl2001

Press1971(Burglary , Outside)


Segrav e&Collins2005(Prop, Catch 3)

Sherman&Rogan1995 (Catch 1)

Wagers2007

-2 -1 0 1 2 3 4 5

Treatment

Catchment


-2 -1 0 1 2 3 4

0.0

0.5

1.0

1.5

2.0

2.5

3.0


Cat

chm

ent O

dds

Rat

io








Monte Carlo re-samples from all permutations

0.7 0.8 0.9 1.0 1.1 1.2 1.3

05

01

001

502

00

Treatment Mean OR (RDM effects)

100

0 M

C r

e-sa

mp

les


0.7 0.8 0.9 1.0 1.1 1.2 1.3

05

01

001

502

00

Catchment Mean OR (RDM effects)

100

0 M

C r

e-sa

mp

les



RCTs only – best case (N=5)

Odds Ratio

Weighted Mean OR (FIXED ef f ects)

Braga 1999 (Recorded Crime)

Braga&Bond2008



Weisburd&Green1995

-2 -1 0 1 2 3 4 5

TreatmentCatchment


-2 -1 0 1 2 3 4

0.0

0.5

1.0

1.5

2.0

2.5

3.0


Ca

tch

me

nt O

dd

s R

atio








RCTs only – worst case (N=4)

Odds Ratio


Braga 1999 (CFS)

Braga&Bond2008



-2 -1 0 1 2 3 4 5

TreatmentCatchment


-2 -1 0 1 2 3 4

0.0

0.5

1.0

1.5

2.0

2.5

3.0


Cat

chm

ent O

dds

Rat

io








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 non-significant 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


Thank you for your attention

Lucia [email protected]

2010 International NPIA-Cambridge Conference on Evidence-Based Policing

ucl department of security and crime science systematic review of the empirical evidence of spatial...

Documents

extent of crime displacement

threat of crime displacement

relocation of crime

crime placement

crime prevention studies

crime prevention initiative

ucl department of security

extent of displacement