Effectiveness of CCTV in Reducing Crime

Transcription

1 Effectiveness of CCTV in Reducing Crime Campbell Systematic Review Brandon C. Welsh David P. Farrington November 2009

2 Purpose Report on results of updated systematic review and meta-analysis on the effects of CCTV on crime in public space Discuss implications for policy and research Results presented in book: Making Public Places Safer: Surveillance and Crime Prevention (Oxford University Press)

3 Background CCTV: monitoring system that uses video cameras as a means of surveillance (Goold 2004) Control room operation is important CCTV has many claimed advantages Prevention of personal and property crime in public space Assists in interviewing suspects and providing evidence for prosecution Decreases fear of crime Useful especially for terrorism Situational crime prevention measure

4 Formal surveillance (Cornish & Clarke 2003) Enhance or take the place of security personnel Increased use of CCTV in public places in many Western nations, including US In UK, CCTV continues to be single most heavily funded crime prevention method In UK, between 1992 and 2002, more than $500M of public money spent on CCTV

5 In US, public spending on CCTV largely unknown A large number of new surveillance systems, costing at least tens and probably hundreds of millions of dollars, are being simultaneously installed around the country as part of homeland security grants (Boston Globe 2007) Much debate about effectiveness of CCTV to prevent crime and hence, on the wisdom of spending large sums of money

6 To address concerns, British Home Office commissioned first systematic review of CCTV (Welsh & Farrington 2002) Main results: CCTV had an overall small and nonsignificant effect on crime, was most effective in car parks, and had only a small effect on crime in city/town centers and public transportation A national evaluation of CCTV in UK soon followed in 14 sites (Gill & Spriggs 2005) Results were highly concordant with our systematic review (see later)

7 How might CCTV reduce crime? Potential offenders are deterred by their increased subjective probability of detection (but only if crime is committed rationally: impulsive or compulsive crimes, or crimes committed under the influence of drink or drugs, not affected) May increase true probability of detection May increase pedestrian usage of places May encourage potential victims to take security precautions May direct police and security personnel to intervene (Armitage et al. 1999)

8 Other Effects of CCTV It could give victims a false sense of security so they take fewer precautions It may encourage increased reporting to police and increased recording of crime It may cause crime to be displaced to other locations, times or victims Potential offenders need to be aware of cameras (need publicity, coverage, visibility)

9 Methods Systematic review An epidemiological look at the methodology and results sections of a specific population of studies to reach a research-based consensus on a given study topic (Johnson et al. 2000) Use rigorous methods for locating, appraising, and synthesizing evidence from prior evaluation studies Reported with same level of detail that characterizes high quality reports of original research

10 Criteria for inclusion of evaluation studies: CCTV was main intervention Outcome measure of crime Evaluation design of high methodological quality Minimum design: quasi-experimental, with comparable experimental and control areas and before and after measures of crime At least 20 crimes in both areas at pretest

11 Search strategies: Electronic bibliographic databases Literature reviews on CCTV Bibliographies of CCTV reports Contacts with leading researchers Published and unpublished reports Not limited to English language Searches conducted to end of 2006

12 Coding of studies Author, date, location Context of intervention Camera coverage, no. of cameras Monitoring, duration of intervention Sample size Other interventions Outcome measure, data source Research design, before-after time period Results Displacement/diffusion

13 Cambridge Evaluation CCTV implemented in main city center in 1997: secondary center is control area Before-after police records: crime decreased by 14% in experimental area but by 27% in control area (sig diff) Before-after surveys of pedestrians: crime increased by 8% in experimental area and by 19% in control area (not sig diff) Conclude: no evidence of desirable effect

14 National Evaluation 14 projects in city/town centers, residential areas and car parks CCTV effective in car parks: crime decreased 70% CCTV not effective anywhere else Effectiveness of CCTV depends on coverage of the cameras and other interventions such as improved lighting and security arrangements No displacement of diffusion of benefits Belief in effectiveness of CCTV decreases after it is implemented

15 Results Descriptive 95 evaluations identified 93 obtained and analyzed 44 met inclusion criteria 49 did not (excluded) mostly because there was no comparable control area

16 44 included evaluations were implemented in 4 main settings: City/town centers (n=22) Public housing (n=9) Public transport (n=4) Car parks (n=6) Other: 2 residential, 1 hospital

17 Table 1 CCTV Evaluations in City and Town Centers (n=22) Author, Publication Date, and Location Camera Coverage or Number of Cameras Monitoring and Duration of Intervention Sample Size Other Interventions Outcome Measure and Data Source Research Design and Before-After Time Period Blixt (2003), Malmö (Möllevång Square), Sweden 100% coverage Passive monitoring by security personnel E=city square C1=rest of city center C2= areas adjacent to city square Social improvement programs (begun years prior) Violent crime (assault, serious assault, robbery); police records Before-after, experimental-control Before=36 months After=12 months

18 Rating of effectiveness (N=44) Desirable effect (marked decrease in crime): 22 Undesirable effect (marked increase in crime): 11 Null effect (clear evidence of no effect on crime): 7 Uncertain effect (unclear evidence of an effect on crime): 4

19 Meta-analysis A statistical summary of comparable effect sizes reported in each evaluation A comparable measure of effect size and an estimate of its variance are needed in each program evaluation Odds ratio (OR) effect size used Indicates proportional change in crime in C compared with E 41 of 44 studies provided requisite data

20 Setting City/town center (n=22) 17 in UK, 3 in US, Sweden, Norway Few reported camera coverage 14 used active monitoring; 4 passive (watched recording afterwards) 6 used other interventions

21 City/town center (cont.) Meta-analysis (n=20) Small and non-significant desirable effect on crime OR=1.08 (CI , ns), 7% reduction 15 UK studies Slightly larger reduction (10%) OR=1.11 (CI , ns)

22 Public housing (n=9) 7 in UK, 2 in US 6 reported camera coverage: 9-87% All used active monitoring 3 used other interventions

23 Public housing (cont.) Meta-analysis (n=8) Small and nonsignificant desirable effect on crime OR=1.07 (CI , ns), 7% reduction

24 Public transport (n=4) All in underground railway systems 3 in London Underground and 1 in Montreal Metro None reported on camera coverage; no. of cameras reported All used active monitoring 3 used other interventions

25 Public transport (cont.) Meta-analysis (n=4) Sizeable but nonsignificant desirable effect on crime OR=1.30 (CI , ns), 23% reduction Large overall effect: substantial reduction in robberies and thefts in Burrows (1980)

26 Car parks (n=6) All implemented in UK 2 reported camera coverage: % 5 used active monitoring All used other interventions

27 Car parks (cont.) Meta-analysis (n=6) Large and significant desirable effect on crime OR=2.03 (CI , p=.0003), 51% reduction

28 Crime type Major crime types reported: violence (including robbery) and vehicle crimes (including thefts of and from) Violence (n=23) No effect: OR=1.03 (CI , ns) Vehicle crimes (n=22) Large and significant desirable effect on crime OR=1.35 (CI , p=.004), 26% reduction

29 Country comparison Evidence that the use of CCTV was more effective in UK than in other countries UK (n=34) Sizeable and significant desirable effect on crime OR=1.24 (CI , p=.0005), 19% reduction Other countries (n=7) No effect on crime OR=0.97 (CI , ns)

30 Pooled effects All 41 studies Significant desirable effect on crime OR=1.19 (CI , p=.0008), 16% reduction

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32 Displacement and diffusion Most schemes showed that displacement did not occur in city center and public housing Displacement and diffusion rarely measured in public transport and car parks

33 Social Costs Important to investigate potential social costs associated with CCTV and weigh costs against any crime reduction benefits 2 major issues confront proper uses and limits of public area CCTV (von Hirsch 2000) 1. Privacy concerns Expand to include other social costs that may infringe on public interests or violate legal or constitutional protections 2. Legitimising role of crime prevention To what extent does crime prevention legitimise impinging on any interests of privacy or anonymity in public space?

34 Car Parks May be little resistance to the installation of CCTV cameras Because public space is utilized for one rather inconsequential purpose Also, car park is a well defined and clearly marked physical space One could take issue with CCTV cameras in car parks On balance, the crime reduction benefits of the use of CCTV in car parks may outweigh social costs

35 Other public settings Evokes more resistance on the basis of threats to privacy and other civil liberties Associated with a larger number of social harms, including: Fortress society Social exclusion of marginalized populations (Clarke 2000) These settings are at the center of the debate over how best to strike a balance between crime reduction and social costs

36 City and town centers Coverage of cameras is much less than in car parks, but there is often a greater number of cameras extending over a larger area It is this concentration as well as its widespread use in other public (and private) places that contributed to the estimate that the average Briton is caught on camera about 300 times/day

37 A more targeted approach may go some way toward reducing the pervasiveness of the threat to the general public s privacy and other civil liberties Crime analysis could be used to identify those places that are at greatest risk for certain crimes, which, in turn, could be used to guide the implementation of CCTV Advent of mobile and re-deployable CCTV cameras may make this a more feasible and perhaps less costly option

38 Policy Implications Key questions: Why is CCTV most effective in reducing crime in car parks? What are the lessons for other public settings? What accounts for effectiveness of CCTV in the UK?

39 Success of CCTV in car parks associated with: Combined with other situational measures (e.g. improved lighting, fencing, security guards) Targeted on specific crime type (vehicle crimes) Confined space, high degree of coverage of cameras In national UK evaluation on CCTV, effectiveness was significantly correlated with the degree of coverage of the CCTV cameras, which was greatest in car parks (Farrington et al. 2007)

40 Lessons for CCTV in other public settings Implemented as part of a package of situational measures, not on its own Larger, more open areas may require improved communication links with police or security personnel Targeting crime hot spots within areas

41 Factors that may contribute to difference in effectiveness of CCTV in UK and in other countries: CCTV combined with other situational methods Length of follow-up period Cultural context (e.g. level of public and political support)

42 Limitations Implementation issues Construct validity (fidelity) Statistical power (to detect change) Measurement of displacement/diffusion Focus limited to public area CCTV Other potential benefits Suspect identification/apprehension Prevention of terrorist acts

43 Priorities for Future Research High quality evaluation designs needed; randomized trials possible with mobile cameras Need to have adjacent and non-adjacent areas Need police and survey measures of crime Interview potential offenders Identify active ingredients of effective CCTV schemes Measure intensity of CCTV dose (e.g. degree of coverage) and dose-response relationship Longer follow-up periods Cost-benefit analyses needed

44 Next Steps Further analyses of CCTV Forthcoming article in Justice Quarterly (December 2009) Other forms of public area surveillance: Security guards, place managers (e.g. parking attendants, doormen of apartments), defensible space (natural surveillance) OUP book Forthcoming article in Security Journal