Situational crime prevention what we know and what we are starting to understand
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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?

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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)


  • 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 preventionCrime 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)

(Eck and Guerette, 2011)

(Eck and Guerette, 2011)

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

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

So we know that SCP approaches are by and large promising in terms of crime reduction- what 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?

Figure 1a: Direct Linear Relationship

Figure 1b: Positive relationship with diminishing returns

What influence does intensity have on outcome?

Figure 1c: Positive relationship with a capped outcome at a certain level of intensity

Figure 1d: Positive relationship followed by tail-off of returns

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

Intensity measure explained 62% variance in access via rear burglary ratio; not significant with access via front or 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

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 measures- an “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

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.

Johnson, Bowers and Guerette 2012

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…

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