Crime prevention effects of closed circuit television: a systematic

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Home Office Research Study 252 Crime prevention effects of closed circuit television: a systematic review Brandon C. Welsh and David P. Farrington The views expressed in this report are those of the authors, not necessarily those of the Home Office (nor do they reflect Government policy).

Home Office Research, Development and Statistics Directorate August 2002 Crime prevention effects of closed circuit television: a systematic review Home Office Research Studies The Home Office Research Studies are reports on research undertaken by or on behalf of the Home Office. They cover the range of subjects for which the Home Secretary has responsibility. Other publications produced by the Research, Development and Statistics Directorate include Findings, Statistical Bulletins and Statistical Papers.

The Research, Development and Statistics Directorate RDS is part of the Home Office. The Home Office's purpose is to build a safe, just and tolerant society in which the rights and responsibilities of individuals, families and communities are properly balanced and the protection and security of the public are maintained. RDS is also part of National Statistics (NS).

One of the aims of NS is to inform Parliament and the citizen about the state of the nation and provide a window on the work and performance ... more. less.

of government, allowing the impact of government policies and actions to be assessed. Therefore 3 Research Development and Statistics Directorate exists to improve policy making, decision taking and practice in support of the Home Office purpose and aims, to provide the public and Parliament with information necessary for informed debate and to publish information for future use. First published 2002 Application for reproduction should be made to the Communication Development Unit, Room 201, Home Office, 50 Queen Anne 9s Gate, London SW1H 9AT. © Crown copyright 2002ISBN1 84082 882 X ISSN0072 6435 i Foreword This review summarises the findings of previous studies from both the USA and Britain on the effectiveness of CCTV in crime reduction. Forty six relevant studies were assessed according to strict methodological criteria: that CCTV was the main intervention studied; that there was an outcome measure of crime; that crime levels before and after the intervention were measured; that the studies included a comparable control area. The authors considered only 22 of these surveys to be rigorous enough for inclusion in their meta-analysis. The review draws conclusions on the effectiveness of CCTV generally and on its effectiveness in terms of specific settings (e.g. car parks, public transport or city centres). Overall, the best current evidence suggests that CCTV reduces crime to a small degree. CCTV is most effective in reducing vehicle crime in car parks, but it had little or no effect on crime in public transport and city centre settings. Importantly, the review draws attention to the shortcomings of many of the previous evaluations and highlights common methodological problems that either resulted in their exclusion from the review or in their limited value in the debate. The review includes a useful summary of the knowledge gaps in relation to the impact of CCTV on crime and sets out the key elements needed in future research and evaluation if these questions are to be addressed. Carole F Willis Head of Policing and Reducing Crime Unit Acknowledgements We thank Hugh Arnold, London Borough of Sutton; Professor Trevor Bennett, University of Glamorgan; Professor Jason Ditton, University of Sheffield and Scottish Centre for Criminology; Professor John E. Eck, University of Cincinnati; Professor Lorraine Mazerolle, Griffith University; Professor Sara McLafferty, Hunter College; David Skinns, Doncaster College; Dr Peter Squires, University of Brighton; and Professor Pierre Tremblay, University of Montreal, for providing helpful assistance in obtaining copies of evaluation studies used in this report. Appreciation is also extended to Professor Nick Tilley, Nottingham Trent University, for comments on the proposal for this research; Deborah Friedman, University of Massachusetts Lowell, for help with the collection of reports; Jennifer Wylie, for translation services; and Professor Martin Gill, Leicester University, for helpful comments on the report. Thanks also go to Professor Ross Homel, Griffith University, Australia and Professor Graham Farrell, University of Cincinnati, USA, for acting as independent assessors for this report. Brandon C. Welsh David P. Farrington Brandon C. Welsh is an Assistant Professor in the Department of Criminal Justice, University of Massachusetts Lowell. David P. Farrington is Professor of Psychological Criminology in the Institute of Criminology, University of Cambridge. ii Crime prevention effects of closed circuit television: a systematic review Contents Forewordi Acknowledgementsii List of tablesiv List of figuresiv Summaryv 1.Background1 2. Method3 Criteria for inclusion of evaluation studies3 Search strategies5 Key features of evaluations6 Evaluations not meeting inclusion criteria8 3.Results13 City centre or public housing13 Public transport27 Car parks34 Pooled meta-analysis results39 4.Conclusions41 Summary of main findings41 Priorities for research42 Policy implications44 Appendix 1:Literature reviews consulted47 Appendix 2:Evaluation reports that could not be obtained49 References51 iii List of Tables 2.1CCTV evaluations not meeting inclusion criteria9 3.1CCTV evaluations in city centres or public housing15 3.2Meta-analysis of CCTV evaluations in city centres or public housing26 3.3CCTV evaluations in public transport29 3.4Meta-analysis of CCTV evaluations in public transport or car parks34 3.5CCTV evaluations in car parks35 List of Figures 3.1CCTV evaluations40 iv Crime prevention effects of closed circuit television: a systematic review Summary Closed circuit television serves many functions and is used in both public and private settings. The prevention of crime (i.e., personal and property) is among its primary objectives in public space. This report aims to evaluate the evidence on the effectiveness of CCTV in preventing crime. Determining what works to reduce crime requires examination of the results of prior evaluation studies. This is better than drawing conclusions about what works from personal experience, from anecdotal evidence, from widespread beliefs, or from a single study which was well- funded or highly publicised. This is the foundation of an evidence-based approach to preventing crime, and the systematic review represents an innovative, scientific method for contributing to evidence-based prevention of crime. This report has two main objectives: (1) to report on the findings of a systematic review 3 incorporating meta-analytic techniques 3 of the available research evidence on the effects of CCTV on crime, and (2) to inform public policy and practice on preventing crime through the use of CCTV interventions. Systematic reviews use rigorous methods for locating, appraising, and synthesising evidence from prior evaluation studies, and they are reported with the same level of detail that characterises high quality reports of original research. Evaluations meeting the following criteria were included in this review: (1)CCTV was the focus of the intervention (2)there was an outcome measure of crime (3)the evaluation design was of high methodological quality, with the minimum design involving before-and-after measures of crime in experimental and control areas (4)there was at least one experimental area and one comparable control area (5)the total number of crimes in each area before the intervention was at least 20. The following four search strategies were carried out to identify CCTV evaluations meeting the criteria for inclusion in this review: (1)searches of on-line databases (2)searches of reviews of the literature on the effectiveness of CCTV in preventing crime (3) searches of bibliographies of CCTV reports (4) contacts with leading researchers. v Both published and unpublished reports were considered in the searches, and the searches were international in scope and were not limited to the English language. The search strategies resulted in 22 CCTV evaluations meeting the criteria for inclusion. The evaluations were carried out in three main settings: (1) city centre or public housing, (2) public transport, and (3) car parks. Of the 22 included evaluations, half (11) found a desirable effect on crime and five found an undesirable effect on crime. Five evaluations found a null effect on crime (i.e., clear evidence of no effect), while the remaining one was classified as finding an uncertain effect on crime (i.e., unclear evidence of an effect). Results from a meta-analysis provide a clearer picture of the crime prevention effectiveness of CCTV. From 18 evaluations 3 the other four did not provide the needed data to be included in the meta-analysis 3 it was concluded that CCTV had a significant desirable effect on crime, although the overall reduction in crime was a very small four per cent. Half of the studies (nine out of 18) showed evidence of a desirable effect of CCTV on crime. All nine of these studies were carried out in the UK. Conversely, the other nine studies showed no evidence of any desirable effect of CCTV on crime. All five North American studies were in this group. The meta-analysis also examined the effect of CCTV on the most frequently measured crime types. It was found that CCTV had no effect on violent crimes (from five studies), but had a significant desirable effect on vehicle crimes (from eight studies). Across the three settings, mixed results were found for the crime prevention effectiveness of CCTV. In the city centre and public housing setting, there was evidence that CCTV led to a negligible reduction in crime of about two per cent in experimental areas compared with control areas. CCTV had a very small but significant effect on crime in the five UK evaluations in this setting (three desirable and two undesirable), but had no effect on crime in the four North American evaluations. The four evaluations of CCTV in public transportation systems present conflicting evidence of effectiveness: two found a desirable effect, one found no effect, and one found an undesirable effect on crime. For the two effective studies, the use of other interventions makes it difficult to say with certainty that CCTV produced the observed crime reductions. The pooled effect size for all four studies was a non-significant six per cent decrease in crime. vi Crime prevention effects of closed circuit television: a systematic review In car parks, there was evidence that CCTV led to a statistically significant reduction in crime of about 41 per cent in experimental areas compared with control areas. For all of the studies in this setting other measures were in operation at the same time as CCTV. Advancing knowledge about the crime prevention benefits of CCTV schemes should begin with attention to the methodological rigour of the evaluation designs. The use of a control condition is important in ruling out some of the major threats to internal validity, but efforts are also needed to make the experimental and control conditions comparable. Attention to methodological problems or changes to programmes that take place during and after implementation is needed. Statistical power analysis is needed in advance to determine if numbers are sufficient to detect the strength of likely effects. There is also the need for longer follow-up periods to see how far effects persist. Research is needed to help identify the active ingredients and causal mechanisms of successful CCTV programmes and future experiments are needed which attempt to disentangle elements of effective programmes. Research is also needed on the financial costs and benefits of CCTV programmes. Future evaluations need to include alternative methods of measuring crime (surveys as well as police records). The studies included in the present review show that CCTV can be most effective in reducing crime in car parks. Exactly what are the optimal circumstances for effective use of CCTV schemes is not entirely clear at present, and needs to be established by future evaluation research. Interestingly, the success of the CCTV schemes in car parks was limited to a reduction in vehicle crimes (the only crime type measured) and all five schemes included other interventions, such as improved lighting and notices about CCTV cameras. Conversely, the evaluations of CCTV schemes in city centres and public housing measured a much larger range of crime types and the schemes did not involve, with one exception, other interventions. These CCTV schemes, and those focused on public transport, had only a small effect on crime. Could it be that a package of interventions focused on a specific crime type is what made the CCTV- led schemes in car parks effective? Overall, it might be concluded that CCTV reduces crime to a small degree. Future CCTV schemes should be carefully implemented in different settings and should employ high quality evaluation designs with long follow-up periods. In the end, an evidence-based approach to crime prevention which uses the highest level of science available offers the strongest formula for building a safer society. vii Summary viii Crime prevention effects of closed circuit television: a systematic review 1.Background Closed circuit television serves many functions and is used in both public and private settings. The prevention of crime (i.e., personal and property) is among its primary objectives in public space, and this is the focus of the present report. As an intervention targeted at crime, CCTV is a type of situational crime prevention (e.g., Clarke, 1995). According to Clarke and Homel 9s (1997) classification of situational crime prevention, CCTV is viewed as a technique of dformal surveillance d. In this regard, CCTV cameras are seen to enhance or take the place of security personnel. The mechanisms by which CCTV may prevent crime are numerous. These have been articulated by Armitage and her colleagues (1999, pp. 226-27), and are as follows: 3 Caught in the act 3 perpetrators will be detected, and possibly removed or deterred. 3 You 9ve been framed 3 CCTV deters potential offenders who perceive an elevated risk of apprehension. 3 Nosy parker 3 CCTV may lead more people to feel able to frequent the surveilled places. This will increase the extent of natural surveillance by newcomers, which may deter potential offenders. 3 Effective deployment 3 CCTV directs security personnel to ambiguous situations, which may head off their translation into crime. 3 Publicity 3 CCTV could symbolise efforts to take crime seriously, and the perception of those efforts may both energise law-abiding citizens and/or deter crime. 3 Time for crime 3 CCTV may be perceived as reducing the time available to commit crime, preventing those crimes that require extended time and effort. 3 Memory jogging 3 the presence of CCTV may induce people to take elementary security precautions, such as locking their car, by jogging their memory. 1 3 Anticipated shaming 3 the presence of CCTV may induce people to take elementary security precautions, for fear that they will be shamed by being shown on CCTV. 3 Appeal to the cautious 3 cautious people migrate to the areas with CCTV to shop, leave their cars, and so on. Their caution and security-mindedness reduce the risk. 3 Reporting changes 3 people report (and/or police record) fewer of the crimes that occur, either because they wish to show the [desirable] effects of CCTV or out of a belief that dthe Council is doing its best d and nothing should be done to discourage it. The growth in the use of CCTV to prevent crime in recent years, especially in the United Kingdom (Norris and Armstrong, 1999) and, surprisingly to a much lesser extent, in the United States (Nieto, 1997), and the increased attention to research on evaluating its effectiveness against crime (Eck, 1997, 2002; Phillips, 1999), were important reasons for carrying out the present research. Determining what works to reduce crime requires us to examine the results of prior evaluation studies. This is better than drawing conclusions about what works from personal experience, from anecdotal evidence, from widespread beliefs, or from a single study which was well-funded or highly publicised. This is the foundation of an evidence-based approach to preventing crime, and the systematic review (see below), which serves as the basis of this report, represents an innovative, scientific method for contributing to evidence-based prevention of crime. This report has two main objectives: (1) to report on the findings of a systematic review 3 incorporating meta-analytic techniques 3 of the available research evidence on the effects of CCTV on crime, and (2) to inform public policy and practice on preventing crime through the use of CCTV interventions. This report is divided into four chapters. The second chapter reports on the criteria for inclusion of CCTV evaluations in this review and the methods used to search for, code, and analyse evaluation reports of CCTV programmes. The third chapter discusses the research findings organised by the setting in which CCTV evaluations were conducted, and the final chapter summarises the main findings and identifies priorities for future research and policy implications. 2 Crime prevention effects of closed circuit television: a systematic review 2.Method The present report presents a systematic review of the effects of CCTV on crime and follows closely the methodology of this review technique. Systematic reviews use rigorous methods for locating, appraising and synthesising evidence from prior evaluation studies, and they are reported with the same level of detail that characterises high quality reports of original research. According to Johnson et al . (2000, p. 35), systematic reviews dessentially take 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 d. They have explicit objectives, explicit criteria for including or excluding studies, extensive searches for eligible evaluation studies from all over the world, careful extraction and coding of key features of studies, and a structured and detailed report of the methods and conclusions of the review. All of this contributes greatly to the ease of their interpretation and replication by other researchers. It is beyond the scope of this report to discuss all of the features of systematic reviews, but interested readers should consult key reports on the topic (see e.g., Farrington and Petrosino, 2000; Johnson et al ., 2000; Farrington and Welsh, 2001; Farrington et al ., 2001). Criteria for inclusion of evaluation studies In selecting evaluations for inclusion in this review, the following criteria were used: (1)CCTV was the focus of the intervention. For evaluations involving one or more other interventions, only those evaluations in which CCTV was the main intervention were included. The determination of the main intervention was based on the author identifying it as such or, if the author did not do this, the importance of CCTV relative to the other interventions. For a small number of included evaluations with multiple interventions, the main intervention was not identified, but it was clear from the report that CCTV was the most important intervention. It is desirable to include only evaluations where CCTV was the main intervention, because in other cases it is impossible to disentangle the effects of CCTV from the effects of other interventions. (2)There was an outcome measure of crime. The most relevant crime outcomes were violent and property crimes (especially vehicle crimes). 3 (3)The evaluation design was of high methodological quality, with the minimum design involving before-and-after measures of crime in experimental and control areas. The unit of interest is the area (including car parks and underground stations). (4)There was at least one experimental area and one comparable control area. Studies involving residential, business or commercial areas (e.g., city centres), and other public and private areas (e.g., underground stations, car parks) were eligible for inclusion. Studies that compared an experimental area with the remainder of a city were excluded, because the control area was non- comparable. (5)The total number of crimes in each area before the intervention was at least 20. The main measure of effect size was based on changes in crime rates between the before and after time periods. It was considered that a measure of change based on an N below 20 was potentially misleading. Also, any study with fewer than 20 crimes before would have insufficient statistical power to detect changes in crime. The criterion of 20 is probably too low, but we were reluctant to exclude studies unless their numbers were clearly inadequate. It is worth saying a few more words about criterion 3. Ideally, the dgold standard d of the randomised experiment, which is the most convincing method of evaluating crime prevention programmes (Farrington, 1983), would have been used. The key feature of randomised controlled trials, which are widely used in medical evaluations, is that the experimental and control groups are equated before the experimental intervention on all possible extraneous variables. Hence, any subsequent differences between them must be attributable to the intervention. Technically, randomised experiments have the highest possible internal validity in unambiguously attributing an effect to a cause (Shadish et al ., 2002). The randomised experiment, however, is only the most convincing method of evaluation if a sufficiently large number of units is randomly assigned to ensure that the experimental group is equivalent to the control group on all possible extraneous variables (within the limits of statistical fluctuation). As a rule of thumb, at least 50 units in each category are needed. This number is relatively easy to achieve with individuals but very difficult to achieve with larger units such as areas, as in the evaluation of CCTV schemes. For larger units such as areas, the best and most feasible design usually involves before-and-after measures in experimental and control conditions together with statistical control of extraneous variables (Farrington, 1997). The use of a control condition that is comparable with the experimental condition is necessary in order to exclude threats to internal validity. 4 Crime prevention effects of closed circuit television: a systematic review Search strategies The following four search strategies were carried out to identify CCTV evaluations meeting the criteria for inclusion in this review: (1)searches of on-line databases (see below) (2)searches of reviews of the literature on the effectiveness of CCTV in preventing crime (for a list of reviews consulted, see Appendix 1) (3)searches of bibliographies of CCTV reports (4)contacts with leading researchers (see Acknowledgements). Both published and unpublished reports were included in the searches. Furthermore, the searches were international in scope and were not limited to the English language (one non- English language evaluation report is included in the review). Searches (1) through (3) were completed in January 2001 and reflect material published or known up to 31 December 2000. The following eight databases were searched: (1)Criminal Justice Abstracts (2)National Criminal Justice Reference Service (NCJRS) Abstracts (3)Sociological Abstracts (4)Social Science Abstracts (SocialSciAbs) (5)Educational Resources Information Clearinghouse (ERIC) (6)Government Publications Office Monthly Catalog (GPO Monthly) (7)Psychology Information (PsychInfo) (8)Public Affairs Information Service (PAIS) International These databases were selected because they had the most comprehensive coverage of criminological, criminal justice, and social science literatures. They are also among the top databases recommended by the Crime and Justice Group of the Campbell Collaboration, and other systematic reviews of interventions in the field of crime and justice have used them (e.g., Petrosino, 2000; Petrosino et al ., 2000). The following terms were used to search the eight databases noted above: closed circuit television, CCTV, cameras, social control, surveillance, and formal surveillance. When applicable, dcrime d was then added to each of these terms (e.g., CCTV and crime) to narrow the search parameters. 5 Method These search strategies resulted in the collection of 22 CCTV evaluations meeting the criteria for inclusion in this review. A few of the evaluations identified, which may or may not have met the criteria for inclusion, could not be obtained. The reports of these evaluations are listed in Appendix 2. Key features of evaluations Tables 3.1, 3.3, and 3.5 summarise key features of the 22 included CCTV evaluations. Ï Author, publication date, and location. The authors and dates of the most relevant evaluation reports are listed here, along with the location of the programme. The evaluations have been listed in chronological order, according to the date of publication. Ï Context of intervention. This is defined as the physical setting in which the CCTV intervention took place. Ï Type and duration of intervention. The intervention is identified and any key features are listed. The length of time the programme was in operation is also noted here. Ï Sample size. The number and any special features of the experimental and control areas are identified. Ï Other interventions. Interventions other than CCTV which were employed at the time of the programme are identified. Ï Outcome measure of interest and data source. As noted above, crime was the outcome measure of interest to this review. Here the specific crime types as well as the data source of the outcome measure are identified. Ï Research design and before-after time period. As noted above, the minimum research design for an evaluation to be included in this review involves before- and-after measures of crime in comparable experimental and control areas. If matching or other statistical analysis techniques were used as part of the evaluation of programme effects, these too are noted here. The before and after time periods of the evaluation are also noted. 6 Crime prevention effects of closed circuit television: a systematic review Ï Results. In summarising results, the focus was on the most relevant crime outcomes for this review (i.e., property and violent crime types) and comparisons between experimental and control areas. The results of significance tests are listed, but they were rarely provided by researchers. Similarly, few effect size measures were provided. The problem with significance tests is that they depend partly on sample size and partly on strength of effect. A significant result in a large sample could correspond to a rather small effect size, and conversely a large effect size in a small sample may not be statistically significant. Consequently, this report relies on measures of effect size (and associated confidence intervals) where possible. Each of the evaluations were rated on their effectiveness in reducing crime. Each evaluation is assigned to one of the following four categories: (1)desirable effect: significant decrease in crime (2)undesirable effect: significant increase in crime (3)null effect: clear evidence of no effect on crime (4)uncertain effect: unclear evidence of an effect on crime. Category 4 was assigned to those evaluations in which methodological problems (i.e., small numbers of crimes or contamination of control areas) confounded the reported results to the point that the evaluation could not be assigned to one of the other three categories. It was difficult to rate those evaluations which reported the percentage change in crime (from before to after the programme was implemented), but did not provide data on the number of crimes in the before and after periods. Instead of giving these evaluations a rating of duncertain effect d, they were rated subjectively on the basis of the reported percentage change in crime. Ï Other dimensions. CCTV evaluations differ on many different dimensions, and it is impossible to include more than a few in summary tables. Two important issues that are addressed, not in the tables, but in the accompanying text, are displacement and diffusion of benefits. Displacement is often defined as the unintended increase in targeted crimes in other locations following from the introduction of a crime reduction scheme (for a discussion of dbenign d or desirable effects of displacement, see Barr and Pease, 1990). Five different forms of displacement have been identified by Reppetto (1976): temporal (change in time), tactical (change in method), target (change in victim), territorial (change in place), and functional (change in type of crime). Diffusion of benefits is defined as the unintended decrease in non-targeted crimes following from a crime reduction scheme, or the dcomplete reverse d of displacement (Clarke and Weisburd, 1994). 7 Method In order to investigate territorial displacement and diffusion of benefits, the minimum design involves one experimental area, one adjacent area, and one non-adjacent control area. If crime decreased in the experimental area, increased in the adjacent area, and stayed constant in the control area, this might be evidence of displacement. If crime decreased in the experimental and adjacent areas and stayed constant or increased in the control area, this might be evidence of diffusion of benefits. Very few of the included evaluations had both adjacent and non-adjacent but comparable control areas. More had an adjacent control area and the remainder of the city as another control area, for example. Evaluations not meeting inclusion criteria When coding CCTV evaluations, many did not meet the criteria for inclusion and thus have not been included in the present review. Altogether, 24 CCTV evaluations were excluded. Table 2.1 lists these evaluations, summarises their key features, and identifies the reasons for exclusion. The reasons for discussing these evaluations here are two-fold: first, it conforms with the widely-held practice in systematic reviews of listing excluded studies and second, it allows readers to judge for themselves the strength of observed effects in excluded evaluations compared with those included. As shown in Table 2.1, 17 of the 24 evaluations were excluded because no control area was used in evaluating the impact of the intervention. Another four evaluations were excluded because no comparable control area was used. The remaining three evaluations (King 9s Lynn, in Brown, 1995; Squires, 1998b, d) were excluded because they did not report crime data. Missing information on the few key features listed in Table 2.1 was not much of a problem with the 24 evaluations, although three failed to specify the length of the follow-up period. For the 21 evaluations that did provide information on the follow-up period, nine involved follow-ups of less than one year. Many of the CCTV schemes appeared to be successful in reducing a range of crimes, including robbery, assault, burglary, motor vehicle theft and vandalism. However, a number of the evaluations of these schemes were limited by small numbers of crimes. Because of methodological problems it is difficult to give much credence to the results of these evaluations. 8 Crime prevention effects of closed circuit television: a systematic review 9 Method Table 2.1:CCTV evaluations not meeting inclusion criteria Author, publication Reason for notOtherSampleFollow-up and date, and locationincluding programmeinterventionssizeresults Burrows (1991)No control areaChanges in store1 store (Tesco --n.a.; design and large retailer) cunknown losses d: proceduresapprox. £12,000 to £5,000 per week; cash losses (from tills): approx. £500 to £20 per week National Association of No control arean.a.1892 years; Convenience Stores, conveniencerobbery: -15.2% (1.58 to 1.34 multiple sites, (1991), USAstoresper store per year, NS) Poyner (1992), No control areaMedia publicity 5 buses8 months; North Shieldsand school visitsvandalism: -52.9% (51 to 24) Carr and Spring (1993), No control areaMultiple (e.g.,Train, tram, and2 years; Victoria, Australiaimproved lighting,bus systems ofcrimes against persons: -42.2% police)Public Transport(57.3 to 33.1 per month); Systemvandalism: -83.6% (700 to 115 broken windows, weekly average) Tilley (1993a), SalfordNo control areaNone3 businesses12 months; total crimes: -14.3% (35 to 30) 1. Tilley (1993b), No control areaMedia publicity1 station car park4 months; Lewishamand notices vehicle crimes: -75.0% (24 to 6) of CCTV 2. Tilley (1993b), HullNo comparable controlNoneE=1 car park,8 months; areaC=city centre asE vs C: theft of vehicles: -88.9% (27 a wholeto 3) vs -5.6% (430 to 406); theft from vehicles: -76.3% (38 to 9) vs +2.8% (961 to 988) 10 Crime prevention effects of closed circuit television: a systematic review Author, publication Reason for notOtherSampleFollow-up and date, and locationincluding programmeinterventionssizeresults 3. Tilley (1993b), No comparable controlNotices of CCTVE=1 car park, 13 months; WolverhamptonareaC=subdivision as E vs C: theft of vehicles: -18.2% (11 a wholeto 9) vs +3% (data n.a.); theft from vehicles: -46.4% (28 to 15) vs -3% (data n.a.) Chatterton and Frenz No control areaNotices of CCTV15 housing5-10 months; (1994), Merseysideschemes ( cshelteredburglary (completions and attempts): accommodation c)-78.8% (4.25 to 0.9 per month) a Davidson and Farr No control areaMultiple (e.g.,5 housing blocks15 months; (1994), Mitchelhill Estate, target hardening, total crime b : -63.1% (28.7 to 10.6 Glasgowlocal management)average per quarter year) Brown (1995), No crime data forNoneE=car parks and32 months; King 9s Lynnexperimental or control adjacent streets, E vs C: theft of vehicles: decline areasC=rest of police (data n.a.) vs ? (data n.a.); theft divisionfrom vehicles: decline (data n.a.) vs decline (data n.a.); burglary (data n.a.) vs ? (data n.a.) Squires and Measor No comparable control NoneE=police beats 1-4,12 months; (1996), BrightonareaC=rest of BrightonE vs C: total crimes: cunder c -10% (data n.a.) vs -1% (data n.a.) Bromley and Thomas No control areaMultiple (e.g.,Different types ofn.a. (no before measures); (1997), Cardiff and staff at exits,car parksvehicle crimes: Cardiff (8.3/100 Swanseapainting)spaces) vs. Swansea (13.7/100 spaces) Gill and Turbin (1998, No control areaNone2 retail storesn.a.; 1999), Leeds and stock losses from theft (before-during Sheffieldphases and Leeds store only): £600 to £200 per week 11 Method Squires (1998b), No crime data for NoneE=town centre 8 months; E vs C: total crime: Burgess Hillcontrol area(beat 1), C=beat 1 -37.2% (data n.a.) vs ? (data n.a.) excluding surveillance area Squires (1998c), No comparable controlNoneE1=town centre6 months; Crawleyarea(beat 1), E2=E1 + E1 vs C: total crimes: -12% (data 3 shopping parades;n.a.) vs -3% (data n.a.) C=rest of Crawley Squires (1998d), No crime data forNoneE=town centre 8 months; East Grinsteadcontrol area(beat 1), C=beat 1 E vs C: total crime: -25.6% (data excluding n.a.) vs ? (data n.a.) surveillance area Beck and Willis (1999), No control areaNone15 stores: E1=3 6 months; multiple siteshigh level system; theft (by staff and customers): c E2=6 medium level,E1=+37.8% (1.96% to 2.70%), E3= 6 low levelE2=-17.9% (2.40% to 1.97%) E3=-26.6% (2.63% to 1.93%) Ditton and Short (1999) No control areaNone28 police beats in12 months; and Ditton et al. (1999), city centretotal crimes: +9% (data n.a.) Glasgow 1. Sivarajasingam and No control areaNone1 city centre or2 years; Shepherd (1999), town areaA&E recorded assault: -11.5% Cardiff(7,066 to 6,251); police-recorded assault: +20.8% (677 to 818) 2. Sivarajasingam and No control areaNone1 city centre or2 years; Shepherd (1999), town areaA&E recorded assault: +3.0% Swansea(3,967 to 4,086); police-recorded assault: -34.0% (486 to 321) 12 Crime prevention effects of closed circuit television: a systematic review Author, publication Reason for notOtherSampleFollow-up and date, and locationincluding programmeinterventionssizeresults 3. Sivarajasingam and No control areaNone1 city centre or2 years; Shepherd (1999), Rhyltown areaA&E recorded assault: +46.0% (1,249 to 1,823); police-recorded assault: -24.0% (526 to 400) 1. Taylor (1999), No control areaMultiple (e.g.,154 businesses11 months; Leicester (West End)silent alarm)commercial burglary: decline (data n.a.) 2. Taylor (1999), No control areaMultiple (e.g.,n.a.24 months; Leicester (Belgrave)silent alarm)commercial burglary: decline (data n.a.) aThe total number of offences were 51 in the before period and 9 in the after period. cIn 13 of the 15 schemes, no offenses of burglary were recorded for the period after CCTV was installed. One scheme had no burglaries in either period, and in another, there was a slight increase aft er camera installation c (Chatterton and Frenz, 1994, p. 136). bThe individual crimes and their before-after comparisons (average per quarter year) were as follows: burglary (19.0 to 5.4), t heft of and from vehicles (4.7 to 1.4), theft other (2.0 to 2.2), vandalism (2.3 to 0.8), and crimes against the person (0.67 to 0.8). The before and after perio ds consisted of six quarters or 18 months and 5 quarters or 15 months, respectively. cThe figures in parentheses reflect the cvalue of goods lost expressed as a percentage of all goods sold c (Beck and Willis, 199 9, p. 257). Notes: Locations were in the UK unless otherwise specified; E = experimental area; C = control area; n.a. = not available; A&E = accident and emergency department; NS = non-significant. 3.Results This chapter discusses the results of the 22 included CCTV evaluations. It also summarises key features of the evaluations which are important in the assessment of programme effects (e.g., other interventions, sample size, follow-up periods). The evaluations have been organised according to the setting in which the intervention took place. Three main settings were delineated: (1) city centre or public housing, (2) public transport, and (3) car parks. City centre or public housing Thirteen evaluations were identified that met the methodological criteria for inclusion in this review and assessed the impact of CCTV on crime in the setting of a city centre (N=11) or public housing (N=2). Three of the evaluations are reported in Mazerolle et al . (2000). Of the three settings, this contains the largest number of evaluations. Selected evaluations are discussed below and see Table 3.1 for summary information on each of the 13 evaluations. Seven of the 13 evaluations were carried out in England, five in the U.S., and one in Scotland. On average, the duration of the follow-up evaluations was 10.9 months, ranging from a low of three months in the evaluation by Musheno et al . (1978) to a high of 24 months in the evaluations by Short and Ditton (1995) and Skinns (1998b). Only one of the evaluations (Skinns, 1998a) included other interventions in addition to the main intervention of CCTV. Many of the evaluations used multiple experimental areas (e.g., police beats, apartment buildings), meaning that the coverage of the CCTV intervention was quite extensive in the city or town centre. Multiple control areas (e.g., adjacent police beats, remainder of city) were also used by some of the evaluations. As shown in Table 3.1, the city centre or public housing CCTV evaluations showed mixed results in their effectiveness in reducing crime. Five of the 13 evaluations were considered to have a desirable effect on crime, while three were considered to have an undesirable effect (increased crime). The remaining five evaluations were considered to have a null (clear evidence of no effect; N=4) or uncertain (unclear evidence of an effect; N=1) effect on crime. 13 Two evaluations of city centre CCTV schemes were conducted by Brown (1995). The first evaluation took place in Newcastle-upon-Tyne and involved the installation of 14 CCTV cameras in four police beats in the city centre (the experimental area). The control area comprised the seven remaining police beats of the city centre, which surrounded the experimental area. It is important to note that two cameras were installed in police beats which were part of the control area. Fifteen months after the start of the programme, the monthly average of total crimes was reduced by 21.6 per cent (from 343 to 269) in the experimental area and 29.7 per cent (from 676 to 475) in the control area, which overall was an undesirable effect of CCTV. The measure of total crimes includes burglary, criminal damage, theft of vehicles, theft from vehicles, theft other, and juvenile disorder. Table 3.1 presents the results of the intervention for a number of these crimes. Reductions were observed in burglary, theft of vehicles, and theft from vehicles in both the experimental and control areas, with the reductions in the experimental area outpacing those in the control area. However, the number of these crimes in the experimental area was small. For example, burglary was reduced by 57.5 per cent in the experimental area (from 40 to 17) and 38.7 per cent in the control area (from 75 to 46). Brown (1995) found little evidence of territorial or functional (change in type of crime) displacement, but did find some evidence of diffusion of benefits, particularly for the crimes of burglary and criminal damage. The second evaluation by Brown (1995) was carried out in Birmingham. In this programme, 14 CCTV cameras were installed in the centre of the city, with the cameras covering for the most part cshopping streets and partially open market areas c, as well as some of the financial district. Three control areas were established, with streets in control area 1 (C1) receiving partial coverage by the CCTV system (see Table 3.1). Therefore, the experimental area was compared with control areas 2 and 3 combined. After 12 months, total crimes, according to victim survey reports, were reduced in the experimental area, while total crimes increased in each of the three control areas. The actual number of crimes was much greater in the experimental area than in any of the control areas. Some evidence of what appears to be functional displacement (change in type of crime) was found, with offenders switching from robbery and theft from the person to theft from vehicles. In the programme evaluated by Sarno (1995), 11 CCTV cameras were installed in the town centre of the London Borough of Sutton as part of the Safer Sutton Initiative launched in the early 1990s. The remaining part of the police sector in the town centre, which did not 14 Crime prevention effects of closed circuit television: a systematic review 15 Results Table 3.1:CCTV Evaluations in City Centres or Public Housing Author, Publication Context ofType andSampleOtherOutcomeResearch DesignResults Date, and LocationInterventionDuration ofSizeInterventionsMeasure ofand Before- After InterventionInterest andTime Period Data Source Musheno, Levine, PublicCCTVE=3 NoneCrimeBefore-after, E vs C: total and Palumbo housingmonitoringbuildings,(multipleexperimental-crimes: -9.4% (32 (1978), Bronxdale systemC=3offences); controlto 29) vs -19.2% Houses, New York (cameras inbuildingsvictim survey(26 to 21) City, USAlobby andNote: projectBefore=3 months; (uncertain effect) elevators; had 26 After=3 months monitors in high-rises; apartments); 53 3 monthsapartments in each 1. Brown (1995), City or town CCTV; 15 E=4 beats of NoneCrime Before-after, E vs C (monthly Newcastle-upon-Tynecentremonthscentral area,(multiple experimental average): total C=7 Note: 14 of offences); controlcrimes: -21.6% remaining 16 cameras police (343 to 269) vs beats of city are in E; recordsBefore=26 months; -29.7% (676 to centreremaining 2 After=15 months475); burglary: Note: There are in C-57.5% (40 to 17, are 2 other p <.05) vs -38.7% C, but each (75 to 46, p<.05); is less theft of vehicles: comparable 47.1% (17 to 9, to Ep<.05) vs -40.5% (168 to 100, p<.05); theft from vehicles: -50.0% 16 Crime prevention effects of closed circuit television: a systematic review (18 to 9, p<.05) vs -38.9% (106 to 65, p<.05) (undesirable effect) 2. Brown (1995),City or town CCTV; 12E=Area 1 NoneCrime (total Before-after, E vs C1: total Birminghamcentremonths(streets with and most experimental crimes: -4.3% good serious control(163 to 156) vs + coverage), offences); 131.6% (19 to 44) C1=Area 2 victim surveyBefore=12 months; E vs C2: total (streets with After=12 monthscrimes: -4.3% vs + partial 130.8% (26 to 60) coverage), E vs C3: total C2=Area 4 crimes: -4.3% vs + (other streets 45.5% (33 to 48) in Zone A of (desirable effect) Div. F), C3= Area 5 (streets in Zones B-G of Div. F) Sarno (1995, Town centreCCTV; 12 E=part of NoneCrime (total Before-after, E vs C1: total 1996), London monthsSutton town and selected experimentalcrimes (not Borough of Suttoncentre, offences); controlincluding vehicle C1=rest of policecrime): -12.8% Sutton town recordsBefore=12 months; (1,655 to 1,443) centre,After=12 monthsvs -18% (data n.a.) C2=all of E vs C2: total Borough of crimes: -12.8% vs Sutton-30% (data n.a.) (undesirable effect) 17 Results Short and Ditton Town centreCCTV; E=6 policeNoneCrime (total Before-after, E vs C3: total (1995, 1996) and24 monthsbeats, C1=and multiple experimental crimes: -35% (data Ditton and Short rest of 6 categories);controln.a.) vs -12% (1998, 1999),police beats police (data n.a.) Airdrie(not in recordsBefore=24 months;(desirable effect) camera After=24 months vision), C2=Note: Data not rest of police provided to allow sub-division, for comparisons of C3= rest of E with C1 or C2 police division Skinns (1998a, b), Town centreCCTV; E=all or parts 8Help points 9 Crime (total Before-after, E vs C: total Doncaster12 monthsof streets in for public to and selected experimental police-recorded vision of contact CCTV offences); controlcrimes: -21.3% cameras in control police (5,832 to 4,591) commercial roomsrecordsBefore=24 months;vs +11.9% (1,789 areas, After=24 monthsto 2,002) C=comm-(desirable effect) ercial areas Note: There were of 4 adjacent 2 Es and 6 Cs used. townshipsThe C used here is because the author says it was the most comparable to E Note: This E has been used because it includes the other E 18 Crime prevention effects of closed circuit television: a systematic review Squires (1998a), Town centreCCTV; 7E=town NoneCrime (total, Before-after,E vs C: total crimes: Ilfordmonthscentre, violent, and experimental--17% (data n.a.) C=areas selected controlvs +9% (data n.a.) adjacent to offences); (desirable effect) town centrepolice Before=6 months; recordsAfter=7 months Note: 2 other Cs used, but less likely to be comparable to E Armitage, Smyth, Town centreCCTV; 20E=police NoneCrime (total Before-after,E vs C1: total and Pease (1999), monthsbeats with and multiple experimental-crimes: -28% BurnleyCCTV,offences); control(1,805 to 1,410) C1=beats policevs -1% (6,242 to having a recordsBefore=12 months;6,180); violence: common After=12 months a -35% (117 to 87) boundary vs -20% (267 to with CCTV 223); vehicle beats,crimes: -48% (375 C2=other to 253) vs -8% beats in (1,842 to 1,706); police burglary: -41% division(143 to 101) vs +9% (2,208 to 2,426) E vs C2: total crimes: -28% vs +9% (1,069 to 1,175); violence: -35% vs 0% (32 to 32); vehicle crimes: 19 Results -48% vs -8% (309 to 285); burglary: -41% vs +34% (366 to 555) (desirable effect) 1. Mazerolle, City centreCCTV; 3 E=1 site with NoneCalls for Before-after,E vs C (weekly Hurley, and monthsCCTV, C=serviceexperimental-average): +1.8% Chamlin (2000), 1,000 foot (weekly control(901 to 917) vs Cincinnati radius BZaverage); 0% (36 to 36) (Northside), USApolice Before=23 months;(null effect) recordsAfter=6 months Note: 2 other Cs of 200 and 500 foot radii were used and are included in the 1,000 foot radius C 2. Mazerolle, City CCTV; 3E=1 site withNoneCalls for Before-after,E vs C (weekly Hurley, and centre/parkmonthsCCTV, C=service experimental-average): +9.8% Chamlin (2000), 1,000 foot (weekly control(1,062 to 1,166) Cincinnati (Hopkins radius BZaverage); (vs 0% (22 to 22) Park), USApolice Before=23 months;(null effect) recordsAfter=4 months Note: 2 other Cs of 200 and 500 foot radii were used and are included in the 1,000 foot radius C 20 Crime prevention effects of closed circuit television: a systematic review 3. Mazerolle, City centreCCTV; 2 E=1 site withNone Calls for Before-after,E vs C (weekly Hurley, and monthsCCTV, C=service experimental-average): +16.9% Chamlin (2000), 1,000 foot (weekly control(1,005 to 1,175) Cincinnati (Findlay radius BZaverage); vs +17.1% (111 Market), USApolice Before=24.5 months;to 130) recordsAfter=3.5 months(null effect) Note: 2 other Cs of 200 and 500 foot radii were used and are included in the 1,000 foot radius C Williamson and Public CCTV; 18E=9 buildings NoneCrime (total Before-after,E vs C: change in McLafferty (2000), housingmonths(1,220 apart-and multiple experimental-total crimes inside Brooklyn, New ments; Albany categories) control withprojects: 0% vs York, USAproject), inside housing matching-5.3%; change in C=no. of projects and total crimes inside buildings n.a. inside zones Before=18 months;0.1 mile BZ: 0% (Roosevelt of 0.1 to 0.5 After=18 monthsvs -4.0%; change project)miles radii in major felonies around inside projects: projects; -22.8% vs -14.5%; police recordschange in major felonies inside 0.1 mile BZ: -6.4% vs -8.6% (data n.a.) (null effect) 21 Results Farrington, Bennett, City centreCCTV; 11 E=city centre, NoneCrime (total Before-after,E vs C: total crimes: and Welsh (2002), monthsC= secondary and multiple experimental--13.8% (2,600 to Cambridgecentrecategories);control2,242) vs -26.9% police records(1,324 to 968); Also victimBefore=11 months;violent crimes: survey data After=11 months-6.0% (151 to 142) on crime and vs -33.8% (77 to disorder 51); vehicle crimes: -53.1% (224 to 105) vs -54.0% (250 to 115); percentage victimized: +8.0% (26.4% to 28.5%) vs +19.3% (11.4% to 13.6%) (undesirable effect) aThere was an additional eight months of follow-up, but the authors reported crime data as percentage changes relative to the 1 2-month before period, so it was not possible accurately to calculate the number of incidents for the additional eight months. Notes: Locations were in the UK unless otherwise specified; BZ = buffer zone (area surrounding experimental area); E = experime ntal area; C = control area; n.a. = not available. receive any CCTV coverage, served as the control area. (One other control area was used, but it was not comparable to the experimental area.) Twelve months after the programme began, total police-recorded crime (not including vehicle crime) had decreased by 12.8 per cent in the experimental area but by 18 per cent in the control area. Sarno did not investigate the possibility of displacement or diffusion of benefits. Short and Ditton (1995) evaluated a CCTV scheme in Airdrie town centre, which involved 12 cameras spread over six police beats; this comprised the experimental area, and the comparable control area was the remainder of the six police beats not in camera vision. (Two other control areas were used, but the only data supplied was for the rest of the police division.) After 24 months, total police-recorded crime had decreased by 35 per cent in the experimental area compared with a 12 per cent decline in the control area. Short and Ditton found some evidence of diffusion of crime prevention benefits from the experimental area to the control area. The programme evaluated by Skinns was a cmulti-agency, police-led, town centre system, consisting of 63 cameras located in the commercial centre, multi-storey car parks and main town centre arterial roads c (1998a, p. 176). The programme has been included here, as opposed to in the setting of car parks, because the main focus of the intervention was the town centre. As noted above, another intervention was used: chelp points c were established within the experimental area to aid the public in contacting the main CCTV control room. The experimental area included all or parts of streets in vision of the cameras. (Another experimental area was used but it is included in this experimental area.) The control area includes commercial areas of four adjacent townships. Five other control areas were used, but Skinns noted that these control areas were less comparable with the experimental area than the one used in this present report for experimental-control comparisons. Twenty-four months after the start of the programme, total police-recorded crime had reduced in the experimental area by 21.3 per cent, but it had increased in the control area by 11.9 per cent. The author found no evidence that total crimes were displaced from the experimental area to the control area. The increase in crime in the control area was judged by the author to be due to pre-existing trends. In the programme evaluated by Squires (1998a), an unknown number of CCTV cameras were installed in Ilford town centre to address a range of crime problems; areas adjacent to the town centre served as the control condition. (Two other control areas were used, but their comparability with the experimental area is less likely.) Seven months after the programme began, total police-recorded crime had fallen by 17 per cent in the 22 Crime prevention effects of closed circuit television: a systematic review experimental area, but had increased by 9 per cent in the control area. Squires found some evidence that crimes, particularly robbery and residential burglary, had been displaced from the town centre to adjacent areas (the control area). In the programme evaluated by Armitage and her colleagues (1999), an unknown number of cameras were installed in the town centre of Burnley. The experimental area consisted of police beats in the town centre with CCTV coverage. Two control areas were used. The first comprised those police beats which shared a common boundary with the beats covered by CCTV. The second control area consisted of other police beats in the police division. The first control area was more comparable to the experimental area. After 12 months, the experimental area, compared with the two control areas, showed substantial reductions in violent crime, burglary, vehicle crime, and total crime (see Table 3.1). For example, total incidents of crime fell by 28 per cent (from 1,805 to 1,410) in the experimental area compared with a slight decline of one per cent (from 6,242 to 6,180) in control area 1 and an increase of nine per cent (from 1,069 to 1,175) in control area 2. The authors found evidence of diffusion of benefits for the categories of total crime, violent crime, and vehicle crime, and evidence of territorial displacement for burglary. In the three Cincinnati programmes by Mazerolle et al . (2000) the outcome measure used to evaluate the impact on crime was (weekly average) calls for police service, and the evaluation included one experimental and three control areas, the latter being cbuffer zones c of varying distances around the experimental area. The outcome measure was limited to total calls for police service. The authors also reported on police calls for disorder (disorderly persons, curfew violation, neighbour trouble, noise complaints, and suspicious persons or vehicles) and drugs for the three buffer zones, but not for the experimental site; therefore, comparisons could not be made between experimental and control sites for disorder and drug offences. The impact of CCTV on calls for police service was fairly consistent across the three locations: calls for service increased in the experimental site and increased or remained the same in the three control sites or buffer zones. For the Findlay Market programme, crime also increased in the two farthest buffer zones (500 and 1,000 feet away). Overall, CCTV did not have a desirable effect on calls for service in the experimental sites of the three locations. All of these schemes had a null effect on crime. The authors investigated the possibility of displacement in the Northside and Findlay Market programmes. In Northside, the authors found little or no evidence of displacement, while in Findlay Market, the authors concluded that the cresults tend to suggest some displacement of activity as reflected in calls for service c (Mazerolle et al ., 2000, p. 24). 23 Results In the programme evaluated by Farrington et al . (2002), 30 cameras were installed in Cambridge City centre. The control area was a secondary city centre shopping area (the Grafton centre) where there were no cameras on the streets. Comparing 11 months after the cameras were installed with the comparable 11 month period before, police-recorded crimes had decreased by 13.9 per cent in the experimental area (from 2,600 to 2,242) but by 26.9 per cent in the control area (from 1,324 to 968). Hence, there was an undesirable effect of CCTV on police-recorded crimes. Violent crimes (assault and robbery) also decreased more in the control area, while vehicle crimes (theft of and from vehicles) decreased equally in the experimental and control areas. Interviews were also carried out with quota samples of persons in the areas before and after the CCTV installation, asking them about their victimization (insulted or bothered, threatened, assaulted, or mugged) in the previous 12 months. The percentage victimized increased from 26.4 per cent to 28.5 per cent in the experimental area and from 11.4 per cent to 13.6 per cent in the control area, suggesting that the installation of CCTV had no effect on victimization. These results suggested that CCTV may have had no effect on crime but may have caused increased reporting to and/or recording by the police. Only two evaluations (Musheno et al ., 1978; Williamson and McLafferty, 2000) were identified that met the methodological criteria for inclusion in this review and assessed the impact of CCTV on crime in the setting of public housing. Both of the schemes took place in New York City, but were implemented many years apart: the former in 1976 and the latter in 1998. The research design of the evaluation by Williamson and McLafferty (2000) was particularly rigorous, employing matching techniques to control for pre-existing differences (i.e., size of the housing communities, demographics, and neighbourhood location) between the experimental and control areas. Concerning the research design of the other programme, Musheno et al . (1978) took efforts to make the respondents of the victim survey comparable in the experimental and control areas; for example, half of the residents of the three experimental (all apartments received the intervention) and three control buildings were randomly selected to participate in the survey, which was administered before and after the CCTV intervention. Both of the programmes did not involve interventions other than CCTV, although the application of CCTV differed somewhat between the two evaluations. In the programme by Williamson and McLafferty, cameras were installed at various locations in the experimental project (e.g., all elevators, lobbies, and roofs of buildings, and common areas and building water tanks) and were monitored 3 from a remote location 3 24 hours a day, seven days a week, by uniformed officers of the New York City Police Department. In the other programme, cameras were installed in all of the lobbies and elevators of the experimental buildings, but were monitored by the residents themselves: the cameras ctransmit pictures continuously to 24 Crime prevention effects of closed circuit television: a systematic review every resident 9s television receiver ... The top half of the screen telecasts the lobby and the bottom half shows the inside of the elevator viewed from above. Sounds emitted in these locations are also communicated to tenants 9 sets c (Musheno et al ., 1978, p. 648). Another difference between the two evaluations is the scale of the intervention, for both the number of CCTV cameras installed and the number of experimental sites used. In the evaluation by Williamson and McLafferty, a total of 105 cameras were installed at nine buildings (the experimental project), comprising a total of more than 1,200 apartments; in the evaluation by Musheno et al ., three buildings, comprising a total of just over 150 apartments, were used as the experimental site (see Table 3.1). The authors did not report the number of cameras used, but considering that cameras were only installed in the lobbies and elevators, it is likely that the numbers were quite low. The evaluation by Musheno et al . showed that, three months after the cameras were installed, total incidents of crime were reduced in both the experimental and control sites: -9.4 per cent and -19.2 per cent, respectively. However, as illustrated in Table 3.1, the number of crimes recorded was very low. This has the effect of inflating the before-after percentage changes and limiting the examination of programme results to total crimes (the numbers for individual crime types are even smaller). Because of small numbers, it was concluded that this programme had an uncertain effect on crime. The authors did not investigate the possibility of displacement or diffusion of benefits, but it is likely that neither occurred. Williamson and McLafferty evaluated the impact of the CCTV intervention 18 months after the start of the programme and focused on crime inside the public housing projects and inside cbuffer zones c of 0.1 to 0.5 miles radii around the projects. (For the buffer zones, only results inside 0.1 mile are reported here, as the intervention is less likely to affect behaviour beyond this point.) The housing project that received the intervention did not show any change in the total number of police-recorded crimes, either inside the project or inside the 0.1 mile buffer zone, while total crime in the control project dropped by 5.3 per cent inside the project and 4.0 per cent inside the 0.1 mile buffer zone. When total crime is disaggregated, a desirable programme effect is observed for major felonies in both experimental and control projects (see Table 3.1). However, the authors noted that cthe substantial decrease in major felonies around both public housing projects seems to be part of a larger downward trend that was occurring not only in Brooklyn but across New York City in the late 1990s c (Williamson and McLafferty, 2000, p. 7). The authors investigated the possibility of displacement and diffusion of benefits and concluded that there is cno clear evidence c of either, cas the change in crime around the two housing projects does not vary predictably with distance c (ibid., p. 7). 25 Results Table 3.2 presents the results of a meta-analysis of the CCTV evaluations in city centres or public housing. In order to carry out a meta-analysis, a comparable measure of effect size is needed in each project. This has to be based on the number of crimes in the experimental and control areas before and after the CCTV intervention, because this is the only information that is regularly provided in these evaluations. Here, the odds ratio is used as the measure of effect size. For example, in Doncaster, the odds of a crime after given a crime before in the control area were 2,002/1,780 or 1.12. The odds of a crime after given a crime before in the experimental area were 4,591/5,832 or 0.79. The odds ratio therefore was 1.12/0.79 or 1.42. This was statistically highly significant (z = 9.24, p<.0001). The odds ratio has a very simple and meaningful interpretation. It indicates the proportional change in crime in the control area compared with the experimental area. In this example, the odds ratio of 1.42 indicates that crime increased by 42 per cent in the control area compared with the experimental area. An odds ratio of 1.42 could also indicate the crime decreased by 30 per cent in the experimental area compared with the control area, since the change in the experimental area compared with the control area is the inverse of the odds ratio, or 1/1.42 here. The odds ratio could only be calculated for nine evaluations, because numbers of crimes were not reported in the Airdrie, Ilford, Brooklyn, or (for the control area) Sutton evaluations. It shows that CCTV had a significant effect on crime in five evaluations: three desirable (Birmingham, Doncaster, and Burnley) and two undesirable (Newcastle and Cambridge). CCTV had no effect on crime in the four North American evaluations (see Table 3.2). Table 3.2:Meta-Ana

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