Situational crime prevention:
what we know and what we are
starting to understand.
Professor Kate Bowers
UCL Department of Security and Crime Science
University College London (UCL)
Overview
• Situational prevention: what we know
– What are situational approaches?
– Which situational approaches show promise?
• How does this vary by context
– What standard of evidence do we have to support this?
• How do we assess and synthesise these
• Situational prevention: what we are starting to
understand
– Timing, intensity and longevity of treatment
– Estimating COST effectiveness
– Does ‘displacement’ happen?
What is Situational Crime Prevention?
• “Situational crime prevention can be characterized
as comprising measures (1) directed at highly
specific forms of crime (2) that involve the
management, design or manipulation of the
immediate environment in as systematic and
permanent a way as possible (3) so as to reduce
the opportunities for crime and increase the risks
as perceived by a wide range of offenders”
Clarke (1983:225)
Situational prevention
Crime can be reduced by employing techniques
that• increase the effort associated with committing an
offence
• increase the risk associated with committing an offence
• reduce the benefits of such action
• reduce provocations that might otherwise precipitate
crime or;
• remove excuses that offenders might otherwise use to
justify criminal action
An example of the power of opportunity
So do SCP measures work?
• Challenges to a reliable evidence base:
– SCP is inherently context-specific so it is hard to apply
experimental designs such as random assignment
– Many schemes rely on “packages” of interventions
– Most evaluations are conducted retrospectively
– Developing concepts such as displacement, cost
effectiveness should be included to be comprehensive
• Guerette (2009) review of 206 SCP evaluations:
• (75%, n = 154 effective); (12%, n = 24 not effective);(6% n = 12, mixed
findings);(8%, n =16 inconclusive)
Effectiveness of place-based intervention evaluations by common place types
Percent of authors’ conclusions (n)
Place Type
Effective
Not effective Mixed findings Inconclusive
Residential (39)
77 (30)
10 (4)
10 (4)
3 (1)
Public ways (52)
62 (32)
12 (6)
19 (10)
8 (4)
Retail (25)
88 (22)
4 (1)
4 (1)
4 (1)
Transport (26)
88 (23)
0 (0)
8 (2)
4 (1)
Recreational (7)
100 (7)
--
--
--
Total (149)
77 (114)
7 (11)
11 (17)
5 (7)
(Eck and Guerette, 2011)
Effectiveness of the most used interventions
Authors’ conclusions % (n)
Intervention
CCTV
Lighting
CPTED
Mixed / other
Access control
Place management
Street redesign
Total
Totals
n (%)
25 (37)
14 (20)
11 (16)
10 (16)
9 (14)
6 (9)
4 (6)
79 (118)
(Eck and Guerette, 2011)
Effective Not effective
59 (22)
55 (11)
94 (15)
93 (14)
92 (13)
89 (8)
67 (4)
74 (87)
14 (5)
15 (3)
Mixed Inconclusive
24 (9)
15 (3)
3 (1)
15 (3)
6 (1)
7 (1)
8 (1)
7 (8)
11 (1)
17 (1)
12 (14)
17 (1)
6 (7)
What is valid evidence?
• These are the author’s conclusions…
• Consider evaluation design
– ‘3’ or more on the ‘Maryland’ scale?
• Level 3: A comparison between two or more comparable units
of analysis, one with and one without the programme.
• Using meta-analytic reviews
– Ensures a standard of evidence
– Systematic searches and inclusion criteria
– Assesses effect sizes independently of authors
conclusion
Evidence from the reviews- street lighting
• Improved street lighting reduced crime by 21
percent in areas receiving intervention compared
to control areas with no improvement
• Improved street lighting does not just affect crime
committed under cover of darkness; it also
demonstrated a significant effect of these
interventions during the daytime.
• Highlights the importance of considering
mechanisms- natural surveillance or
community involvement?
Welsh and Farrington 2008a
Evidence from the reviews- CCTV
• Based on 44 evaluations of the effects of CCTV on
levels of crime in public places.
• Overall the review found that CCTV has a modest
but significant desirable effect on crime.
• However, this depends very much upon the context
and the type of crime addressed.
– effective at reducing vehicle crime, but not at
preventing violence and assault
– particularly effective at reducing vehicle crime within
the context of car parks
• Demonstrates that context matters
Welsh and Farrington 2008b
A meta-meta-analysis?
• We consider five systematic reviews:
– improvements to street lighting (Welsh and Farrington
2008)
– closed circuit television cameras (CCTV, Welsh and
Farrington 2008)
– repeat victimization strategies (Grove et al., 2012)
– Public area surveillance (Welsh et al., 2010)
– neighborhood watch schemes (Bennett et al., 2008).
Cumulative number of studies included, by year of publication
Bowers and Johnson 2013
Individual effect sizes (odds ratios) for each observation
Individual Effect Sizes (ES)
Favors Treatment
Favors Control
0.1
0.2
0.5
1.0
Odds Ratio
2.0
5.0
10.0
Moderator variables
• Systematically coded information on a number of
other factors
–
–
–
–
the year of publication of the evaluation
the country in which the intervention was implemented,
the outcome measured (in terms of crime type)
the physical context of the intervention (e.g. was it
implemented in a residential area, a town center, and
so on).
• Many others would be desirable
– the funding strategy
– the agency context
– Mainstream or pilot project
Weighted mean effect sizes by different moderator variables
Lighting (13)
PAS (11)
CCTV (41)
Intervention
NW (18)
RV (27)
Favors Treatment
Favors Control
0.1
0.2
0.5
1.0
Other (32)
2.0
5.0
10.0
5.0
10.0
5.0
10.0
5.0
10.0
5.0
10.0
Odds Ratio
CarParks (11)
Hotspots (3)
Context
PublicHousing (14)
TownCenter (22)
Residential neighbourhood (28)
Favors Treatment
Favors Control
0.1
0.2
0.5
1.0
2.0
Odds Ratio
Other (6)
Country
AUS (6)
USA (38)
UK (68)
Favors Treatment
Favors Control
0.1
0.2
0.5
1.0
Other (14)
2.0
Odds Ratio
Calls for service (4)
Sexual assault (4)
Crime type
Vehicle crime (10)
Burglary (40)
All crime (38)
Favors Treatment
Favors Control
0.1
0.2
0.5
1.0
2.0
Odds Ratio
2010s (35)
1990s (54)
Decade
1980s (11)
1970s (10)
Favors Treatment
Favors Control
0.1
0.2
0.5
1.0
2.0
So we know that SCP approaches are by and
large promising in terms of crime reductionwhat else should we consider?
•
•
•
•
How much treatment is optimal?
Which approaches are cost effective?
Which approaches are sustainable?
What are the crime ‘spin-offs’ of SCP?
– Displacement
– Diffusion of benefit
How much treatment is optimal:
An Alley-gating example
Outcome analysis
• There was a 33% reduction in the share of burglary in
the action areas relative to the control when all gates
were considered
• This increased to a 37% reduction when only those
gates that had been in place for a year or more were
considered
• This translates to a reduction of 875 burglaries (all
areas) and 727 burglaries (12 months only)
Bowers, K. J., Johnson, S. D.,
and Hirschfield, A. F. G. (2004a).
Intensity Measures
• Input Intensity
– Inputs to the scheme such as equipment and staffing
– Usually expressed in financial terms
e.g. total cost of scheme/no of households
• Output Intensity
– What outputs were actually realised?
e.g. number of locks fitted, offenders completing rehabilitation, number of
hours of rehabilitation provided
– Good for examining the relationship between what was done and
the impact observed
Bowers, K. J., Johnson, S. D., Hirschfield,
A. F. G. (2004b).
What influence does intensity have on
outcome?
8
Figure 1a: Direct Linear
Relationship
Outcome
7
6
5
4
3
2
1
0
0
2
4
6
8
Outcome
Intensity
5
4.5
4
3.5
3
2.5
2
1.5
1
0.5
0
Figure 1b: Positive relationship
with diminishing returns
0
2
4
Intensity
6
8
What influence does intensity have on
outcome?
3.5
Figure 1c: Positive
relationship with a capped
outcome at a certain level of
intensity
Outcome
3
2.5
2
1.5
1
0.5
0
0
2
4
6
8
Intensity
4
Figure 1d: Positive
relationship followed by tailoff of returns
Outcome
3.5
3
2.5
2
1.5
1
0.5
0
0
2
4
Intensity
6
8
Crime reduction and implementation intensity
• 55% and 37% of variance in burglary ratio explained by no of blocks
protected (cumulative and quarterly respectively)
MO analysis
0.45
Historic period
Point of Entry
% of remainder of PFA
0.4
0.35
0.3
0.25
0.2
0.15
0.1
0.05
Ja
nAp 9 8
r9
Ju 8
lO 98
ct
J a 98
nAp 9 9
r9
Ju 9
lO 99
ct
J a 99
nAp 0 0
r0
Ju 0
l-0
O 0
ct
J a 00
nAp 0 1
r0
Ju 1
lO 01
ct
-0
Ja 1
nAp 0 2
r0
Ju 2
lO 02
ct
J a 02
nAp 0 3
r03
0
Intensity measure explained 62% variance in access via rear burglary
ratio; not significant with access via front or other
Back
Front
Other
Alley-gating: Cost Benefit Analysis
•
Assuming:
– cost per gate of £659 (consultation, manufacture, installation)
– average cost to society of one burglary £2,300 (Brand and Price, 2000)
After 12 months, £1.86 return for every pound spent
Cost-benefit analysis of other situational measures
Study
Description
Benefit-cost ratio
Painter and Farrington
(2001)
Installation of improved street lighting in
Dudley and Stoke-on-Trent in the UK
A saving of $6.19 for every dollar
spent in Dudley and a saving of
$5.43 for every dollar spent in
Stoke.
A saving of £5.04 for every pound
spent.
Forrester et al (1990)
Multi-prevention approach to reducing
residential burglary on the Kirkholt
housing estate.
Clarke and McGrath
(1990)
Robbery reduction intervention in betting
shops.
A saving of $1.71 was estimated for
every dollar spent.
Skinns (1998)
Installation of CCTV cameras in
Doncaster, UK
A saving of £3.50 was estimated for
every pound spent.
Gill and Spriggs (2005)
Covered 7 programmes in a national
evaluation of CCTV cameras
Four of the schemes were found to
be cost-effective, the other three
were not.
Sustaining or prolonging treatment effect
• Residual deterrence
– This occurs when a treatment that has been
conducted in an area stops, but the crime reductive
effect continues.
• Has particularly been applied to police crackdown operations
• Anticipatory benefit
– Smith, Clarke & Pease (2002) - evidence of reduction
in crime before physical implementation of measuresan “anticipatory benefit” in 40% of tested cases
Anticipatory benefit
Anticipatory Benefit- 6 Alternative Explanations
•
Preparation- anticipation
– Offenders believe the programme is operational before it actually is
•
Publicity/disinformation
– Offenders believe covert enforcement exists through publicity/rumour
(disinformation)
– Offenders are warned of a crackdown through direct communication (publicity)
•
Preparation- disruption
– Preparation for prevention causes surveillance at prevention sites
•
Creeping implementation
– Part of the response is put into effect before the official start date
•
Preparation- training
– Planning or training make the public/police better prepared to address problems
•
Motivation
– Public/police are more highly motivated which leads to better performance
Publicity Strategies
Crime rate with publicity
Crime rate without publicity
(1) Publicity to enhance scheme impact during
120
100
Implementation activity
Activity
80
(2) Publicity to produce
an anticipatory effect
as well as enhancing (3) Publicity to enhance
scheme impact
both residual detterence
and scheme impacts
during implementation
60
40
20
0
1
2
3
4
5
6
7
8
9
10 11 12 13 14 15
Quarterly time period
Johnson and Bowers 2003
Displacement- an Achilles’ heel?
• One of the most common criticisms of SCP interventions is
that crime will simply relocate to other places or times
• Displacement is the relocation of crime from one place,
time, target, offense, tactic or offender to another as a
result of some crime prevention initiative
– Spatial displacement which is the movement of crime from an intervention
treatment area to an area nearby, is the form most commonly analyzed.
– In its extreme form it could negate or cancel out any scheme effect.
•
On the flip side of the displacement debate is the ‘diffusion of
crime control benefits’ (Clarke and Weisburd 1994).
– Diffusion occurs when reductions of crime are achieved in areas that are close to
crime prevention interventions, even though those areas were not actually targeted
by the intervention itself.
Systematic Review of SCP Displacement/ Diffusion
Guerette and Bowers 2009
Does crime just move elsewhere as a result of SCP? On balance, no.
Best Case
Worst Case
Weisburd&Green(1995)
WaplesEtAl(2008)
Treatment
Treatment
Catchment
WaplesEtAl(2008)
Catchment
Skinns(1998)
Skinns(1998)
Selden (1978)
Selden (1978)
SarnoEtAl(1999)
SarnoEtAl(1999)
Ratclif f eEtAl(2009)
Ratclif f eEtAl(2009)
Lay cock&Austin(1992)
Lay cock&Austin(1992)
Cummings(2005)
Cummings(2005)
CameronEtAl(2008)
CameronEtAl(2008)
Braga and Bond
Braga and Bond
BowersEtAl(2003)
BowersEtAl(2003)
Bowers et al. (2005)
Bowers et al. (2005)
Allat(1984)
Allat(1984)
Weighted Mean OR (RDM ef f ects)
Weighted Mean OR (RDM ef f ects)
Favors Control
-2
-1
0
Favors Control
Favors Treatment
1
2
3
4
Odds Ratio
Johnson, Bowers and Guerette 2012
-2
-1
0
Favors Treatment
1
Odds Ratio
2
3
4
Summary of findings
• On the aggregate, the majority of SCP efforts are reportedly
effective
• Diffusion of benefits is just as likely to occur as displacement
• SCP effects are often compounded by anticipatory benefits.
• On the aggregate cost assessments of SCP measures are less
common
• Little is known about the sustained impact of SCP measures
beyond one or two years.
– Situational prevention measures appear to have more enduring reduction
effects compared to focused policing operations (Braga and Bond, 2008).
Next steps
• More on sustainability/ cost effectiveness
• Extent of forms of displacement other than spatial
• Interaction between the different forms
• Exploring the relationship between dosage and crime
reduction
• Further reviews
• examining the degree to which controlling access to facilities,
reducing anonymity or reducing provocations can reduce crime
• Prioritising individual evaluations
• effectiveness of replacing beer glasses with safer alternatives
• Applicability of SCP to new crime types
Finally situational measures don’t have to be
ugly…