Korea Planning Association
[ Article ]
Journal of Korea Planning Association - Vol. 55, No. 7, pp.46-55
ISSN: 1226-7147 (Print) 2383-9171 (Online)
Print publication date 31 Dec 2020
Final publication date 24 Nov 2020
Received 17 Jul 2020 Reviewed 06 Sep 2020 Accepted 06 Sep 2020 Revised 24 Nov 2020
DOI: https://doi.org/10.17208/jkpa.2020.12.55.7.46

The Analysis of Effectiveness for CPTED Project Using Weighted Displacement Quotient (WDQ)

Son, Dongpil* ; Park, Yuna** ; Hyeon, Taehwan***
*Research Fellow, Architecture and Urban Research Institute dpson@auri.re.kr
**Assistant Research Fellow, Architecture and Urban Research Institute ynpark@auri.re.kr
***Assistant Research Fellow, Architecture and Urban Research Institute thhyeon@auri.re.kr

Correspondence to: ***Assistant Research Fellow, Architecture and Urban Research Institute (Corresponding Author: thhyeon@auri.re.kr)

Abstract

Since the 2000s, central and local governments have continued to push ahead with Crime Prevention Through Environmental Design (CPTED) projects in order to prevent crimes and reduce the public’s fear of crime. Various studies have been conducted of the effectiveness of CPTED projects with the spread of such project, by analyzing the rate of increase and decrease of crime and fear of crime before and after the project. Since then, studies have been conducted on the crime displacement effect and diffusion effect of crime control to nearby areas due to the CPTED project, for which analysis Weighted Displacement Quotient (WDQ) has been applied. This study conducted a WDQ analysis of theft and violent crimes for the CPTED project of the Seoul Metropolitan Government to analyze the crime displacement and diffusion of benefits, confirming that theft crime had the effect of spreading profits to buffer areas, while violent crime data did not confirm the crime displacement or diffusion of benefits. This study is meaningful in verifying that the CPTED project is effective in reducing theft crimes, whose effects spread to surrounding areas. However, for a precise analysis of the sustainability and net effects of the project, it is necessary to establish a methodology and propose a plan that can be applied with various statistical analysis tools in the future.

Keywords:

Crime Prevention through Environmental Design, Effectiveness, Crime Displacement Effect, Diffusion Effect of Crime Control, WDQ

키워드:

범죄예방 환경설계, 효과성 분석, 범죄전이효과, 이익확산효과

Ⅰ. Introduction

1. Background and Purpose of Research

According to the 2018 Social Survey by Statistics Korea, 20.6% of Korean citizens felt that the main factor of anxiety was crime occurrence, which was significantly higher than other areas of social safety. Since the 2000s, the central and local governments have implemented CPTED projects under the Crime Prevention Through Environmental Design approach to reduce fear of crime and to prevent crimes. In particular, local governments have actively enforced CPTED projects following the 2012 Yeomni-dong Salt Way project by the Seoul Metropolitan Government.

Many studies have analyzed the effectiveness of CPTED projects and their widespread implementation. Research analyzing the effectiveness of CPTED projects can be largely divided into studies focused on changes in crime rate based on crime data in the target area, and surveys of fear of crime in the target area before and after the project. Due to difficulties involved in acquiring geographic crime data, most studies have analyzed fear of crime and change in disorder through residential surveys and 112 crime reports. Research on crime displacement, which refers to the relocation of crime to nearby areas under Crime Prevention Through Environmental Design, and the diffusion effect of crime control is hardly available in Korea.

This paper examines the crime prevention effect of CPTED projects using geographic crime data. It analyzes the actual crime prevention effect of CPTED projects, and relates effectiveness to crime type, namely, burglary and violence. In addition, it seeks to verify the crime displacement effect and diffusion effect of crime control, which is the reduction of crime in nearby areas as a result of CPTED projects.


Ⅱ. Theories and Literature Review of WDQ

1. Analysis of Effectiveness of CPTED Projects

According to the National Police Agency, the number of local CPTED projects increased from 305 in 2016 to 1,555 in 2018. Despite this continuous increase, the effectiveness of CPTED projects in crime prevention was not systematically verified due to the difficulties involved in acquiring data on crime occurrence. Most research analyzing crime prevention effectiveness was in the form of analysis of effectiveness in areas in which CPTED projects were implemented, and analysis of effectiveness of the CPTED approach, including the installation of CCTVs.

Kang et al. (2018) investigated trends of crime occurrence and changes in disorder in low-income residential areas where CPTED projects were implemented using crime statistics and 112 crime reports. The results showed that CPTED projects were effective in reducing burglary, but not sexual violence, violence, theft, and murder. In the case of disorder, the positive effects were not as distinct as that of the five major crimes, and differences were observed across regions.

Kim (2007) and Yun (2015) surveyed residents in CPTED project target areas, and analyzed project effectiveness based on residents’ fear of crime before and after implementation. Kim (2007) found that physical constituents such as crime prevention facilities and techniques lowered fear of crime, and strengthened social constituents such as social solidarity and reliability. The strengthened social constituents also helped to reduce fear of crime. That is, CPTED projects were effective in reducing fear of crime in target areas. Yun (2015) showed that CPTED projects lowered crime occurrence and reduced fear of crime. The fear of crime was more strongly influenced by social disorder than physical disorder. As such, efforts should be exerted to prevent social disorder when implementing CPTED projects.

Seo et al. (2018) analyzed the effectiveness of a CPTED project based on indirect factors such as a survey of residents in the target area, interviews with residents, changes in floating population before and after project implementation, and changes in perception of others. The results showed that the floating population increased in the target area, which can be interpreted as a positive effect of the project. However, the floating population decreased one year after the end of the project, which demonstrates that the effect of the project lacks sustainability. Similar results were observed in the survey and interviews. The CPTED project was effective in reducing fear of crime immediately after implementation, but quickly declines in effectiveness if not accompanied by follow-up measures.

Research analyzing the effectiveness of CPTED projects, which aim to reduce crime, is difficult to carry out without the cooperation of the National Police Agency, and most studies tend to rely on indirect measurements of effectiveness.

2. Crime Displacement and Diffusion Effect of Crime Control

The ultimate goal of CPTED projects is to suppress the occurrence of crimes by weakening perpetrators’ crime motivation and imposing constraints on criminal acts through changes in the physical environment of spaces vulnerable to crime and community enforcement. This intervention may result in crime displacement, which is the relocation of crime to nearby areas. As such, the effectiveness of CPTED projects should be evaluated with consideration of the crime displacement effect and the diffusion effect of crime control.

Weisburd et al. (2006) defined crime displacement as “shift of crime either in terms of space, time or type of offending from the original targets of crime prevention interventions.” The six types of crime displacement are: spatial displacement in which perpetrators move from areas where crime is difficult to commit to another location where they face less risks, temporal displacement in which perpetrators shift the timing of their offenses to hours or days seen as less risky, target displacement in which offenders give up well-protected targets and focus on more vulnerable ones, tactical displacement in which perpetrators change the tactics they use to avoid an obstacle designed to thwart their efforts, perpetrator displacement in which other perpetrators take the place of perpetrators who are arrested or give up committing offenses, and crime type displacement in which perpetrators commit entirely different type of offenses when a certain crime is not possible (Barnes, 1995:96).

Meanwhile, crime displacement researchers observed effects that are the complete opposite of displacement. Clarke & Weisburd (1994) referred to the spread of crime reduction benefits beyond the target area as “diffusion of crime control benefits,” and defined it as “the spread of the beneficial influence of an intervention beyond the places which are directly targeted, the individuals who are the target of control, the crimes which are the focus of intervention or the time periods in which an intervention is brought.” The diffusion of benefits occurs when perpetrators are uncertain about the risks of detection and exposure when committing offenses, and when the rewards of certain offenses are weaker than their efforts (Clarke & Weisburd, 1994). Lee & Kim (2009) found that the diffusion of crime control benefits not only suppressed crimes in nearby areas, but also suppressed other types of crime, and could also sustain the effect of crime reduction.

When analyzing the actual effectiveness of crime prevention activities, the analysis should not simply be confined to the target area, but should take into account the possible effects of crime displacement and diffusion of benefits in nearby areas. Past studies on the subject by local and international researchers have mostly relied on the Weighted Displacement Quotient (WDQ) proposed by Bowers & Johnson (2003) to verify the effects of crime displacement and diffusion of benefits.

3. Understanding of WDQ

Bowers & Johnson (2003) developed WDQ as a tool to measure crime displacement effect and diffusion of benefits.

A quasi-experimental design was incorporated as the basic framework of research, and the effects of the experiment were evaluated using a nonequivalent control group design with pretest–posttest. The experimental results were compared for the target area, comparison area, and buffer area (Lee & Kim, 2009:260). The target area is the area in which crime prevention or a CPTED project was implemented. The buffer area is the area expected to be involved in crime displacement as a result of crime prevention activities in the target area. The comparison area, which serves as the control, is unrelated to changes in crime occurring in target and buffer areas. When setting buffer and control areas, it should be noted that the three areas must be homeogenous in terms of geographic properties, demographics, and criminal characteristics to overcome the problem of how variables cannot be controlled between groups (Lee & Kim, 2009:263). The control area must be larger than the target area as a smaller control area would cause severe fluctuations in measurements of crime change rate relative to changes in reference time period. Since the buffer area is set to be within a certain radius of the target area, it is generally larger than the target area (Lee & Kim, 2009:263-264).

Bowers & Johnson (2003) proposed three principles of WDQ. First, the crime change rate of the control area is compared to that of the target area and buffer area, and serves as a criterion in describing the crime displacement effect. Second, spatial displacement to be described by WDQ presumes that crime is displaced from the target area to the buffer area. Third, the occurrence of crime displacement means that the target area sees a decrease in crime due to crime prevention activities, while the buffer area experiences a higher increase in crime than the control area. The WDQ equation below reflects the three principles, and integrates spatial and temporal concepts.

Crime displacement and diffusion of benefits can be verified by comparing changes in the crime rate between the target area and control area, and at the same time, changes in crime rate between the buffer area and control area. According to the above equation, the denominator (A′) represents the effect of crime prevention activities or the CPTED project in the target area. The denominator ((A′)) generally assumes a negative (−) value when crime prevention activities are performed, which demonstrates the effectiveness of such activities in reducing crime. A positive denominator ((A′)) means that the decrease in crime rate in the target area is lower than that of the control area, indicating that crime prevention activities were not effective in reducing crime. The numerator ((B′)) measures the crime displacement effect and diffusion of benefits in the buffer area. A negative (−) value means that crime prevention activities resulted in diffusion of benefits, while a positive (+) value indicates that crime was displaced to nearby areas (Bowers & Johnson, 2003:285).

WDQ can be interpreted in seven ways that are shown in Table 1 depending on the combination of denominator ((A′)) and numerator ((B′)) values. First, a WDQ larger than 1 means that crime prevention activities were effective in reducing crime in the target area, and led to diffusion of benefits. That is, crime prevention activities were largely successful. Second, a WDQ close to 1 means that the diffusion of benefits in the buffer area was similar to the crime prevention effect in the target area. Third, a WDQ between 0 and 1 means that the crime prevention effect in the target area was greater than diffusion of benefits in the buffer area. Fourth, a WDQ of 0 occurs when the numerator ((B′)) is 0, which means that there was no crime displacement or diffusion of benefits. Fifth, a WDQ between 0 and -1 means that crime prevention activities were effective in reducing crime in the target area, but that the buffer area was affected by crime displacement. Sixth, a WDQ close to -1 means that crime prevention activities reduced crime in the target area, but the net effect was neutral considering the crime displacement to the buffer area. Lastly, a WDQ smaller than -1 means that crime prevention activities had the reverse effect of increasing crime (Bowers & Johnson, 2003: 285-286).

Interpretation of the weighted displacement quotient

4. Literature Review and Distinctiveness of Research

Following the introduction of WDQ by Bowers & Johnson in 2003, many studies have applied WDQ to the analysis of crime displacement and diffusion of benefits (Bowers & Johnson, 2003; Park et al., 2011; Lim et al., 2016; Cho & Jung, 2017; Haberman & Stiver, 2018; Park et al., 2018; D. Kim et al., 2019).

1) Research Based on Area Setting

Research based on area setting can be classified into those that set areas based on administrative units, and those that set areas in the form of concentric circles using geographic information systems.

Bowers & Johnson (2003) employed both approaches of setting areas based on administrative units and in the shape of concentric circles. In the former, 21 areas in Northern England were set as target areas, the basics administrative unit containing target areas as the buffer area, and the regional administrative unit as the control area. In the latter, the buffer area was comprised of five concentric circles spaced 400 meters apart, and the change in residential burglary rate was measured for 20 months before and after the implementation of the crime prevention project.

Park et al. (2011) used WDQ to analyze the effectiveness of CCTVs in crime prevention. The target area was a detached house lot in Haan-dong, Gwangmyeong-si where CCTVs were newly installed, the buffer area was Haan-dong, and the control area was comprised of two areas: part of Gwangmyeong 2-dong and 3-dong, and part of Gwangmyeong 6-dong and 7-dong. Lim et al. (2016) analyzed the effectiveness of CCTVs by setting the area within a radius of 100 meters of the CCTV site as the target area, the area within 100 to 250 meters as the buffer area, the area within 250 to 400 meters as the first control area, and the area within 400 to 800 meters as the second control area. Cho & Jung (2017) set Yeomni-dong, Mapo-gu, Seoul as the target area, and nearby neighborhoods similar to Yeomni-dong in area, number of households, and population, namely, Daeheung-dong, Ahyeon-dong, and Yonggang-dong, as buffer areas. Bongcheon- dong, Gwanak-gu and Eungam-dong, Eunpyeong- gu, which showed similar patterns in occurrence of sexual crime to the target area before CPTED implemented, were selected as control areas.

2) Research Based on Crime Type

Park et al. (2011) conducted WDQ analysis for robbery, burglary, and violence. Crime prevention efforts were effective in reducing robbery and burglary, but not violence. They concluded that Crime Prevention Through Environmental Design can be a better alternative to CCTV.

Cho & Jung (2017) chose sexual violence as the main type of crime in their analysis. The results showed that the CPTED project was effective in preventing crime in Yeomni- dong. While some crime displacement occurred in buffer areas of Daeheung-dong and Ahyeon-dong, the effects were smaller than direct effects. The diffusion of benefits to Yonggang- dong was also smaller than direct effects. Lim et al. (2016) divided crime type into serious crime and disorder crime, and performed regression analysis and WDQ analysis to examine each crime in terms of length of month, temporal trend, and seasonal effect. Haberman & Stiver (2018) analyzed the effectiveness and crime displacement of the foot patrol program in Dayton, Ohio. The crime types covered were violent crime, robbery, theft from motor vehicles, auto theft, disorder crime, and total crime. The foot patrol program reduced the crime rate in the target area by about 28%, and diffusion of benefits was not observed.

3) Implications and Distinctiveness of Research

From a review of studies that employed WDQ to measure crime displacement and diffusion of benefits achieved through crime prevention activities, the two key factors to be considered in measuring crime displacement and diffusion of benefits can be summarized as follows.

First, the buffer and control areas in CPTED projects should be areas physically and socially similar to the target area, and set as large as possible. By controlling the various factors influencing WDQ, the reliability of measurements of crime displacement and diffusion of benefits can be improved. The area coverage should be appropriately large as the lower number of crimes in smaller areas may lead to a greater difference in crime change rate before and after crime prevention activities.

Second, when choosing a type of crime for WDQ, it should be the same type of crime targeted by crime prevention activities in the target area. A WDQ analysis was performed on various crime types in past research, and crime prevention efforts were proven effective for burglary and disorder crime, but not violence and other crimes. Since the WDQ analysis of this study aims to demonstrate the effectiveness of CPTED projects, it should be limited to the crime types targeted by CPTED projects in target areas. However, it may be meaningful to analyze other crime types as crime prevention activities may have an impact on unintended crime types.

In past research, buffer and control areas were set within a certain radius of the target area, or the buffer area was set as the administrative unit containing the target area, and the control area as a nearby administrative unit similar in area to the buffer area. This study set the buffer area as an area close to the target area, and not larger than the target area by two times. To ensure a similar physical and social environment, the selected buffer area had a similar building use classification to the target area. In particular, this study excluded areas with apartments, dense concentrations of retail shops, and green space, which were of different physical and social characteristics compared to the target area. The control area also had a similar environment to the target area, and was an area not targeted by the CPTED project. For clear distinction, the control area was set as an area surrounded by major roads. Based on these conditions, the selected buffer and control areas were highly homogeneous to the target area.

Crime type was limited to burglary and violence. While CPTED projects target five major crimes (murder, theft, sexual violence, burglary, violence), there are two few cases of murder, burglary, and sexual violence in the target area for effectiveness analysis. Burglary and violence in high-density residential areas were seen as crimes resulting from break-ins and CPTED projects were analyzed for their effectiveness in reducing housebreaking in residential areas .


Ⅲ. Research Methodology

1. Setting of Target Area

This study analyzed the effectiveness of CPTED projects in consideration of crime displacement and diffusion of benefits. For this purpose, the target area was set as the area in which Project B was implemented by District A.

Seoul has a higher number of crimes than other regions, and many CPTED projects were implemented following the 2012 CPTED project in Yeomni-dong. District A has the highest proportion of single-person households in Seoul, and has seen a high number of burglary and violence due to break-ins. In 2016, District A enacted the Ordinance of Urban Environment Design for Crime Prevention to help prevent crime and lower fear of crime. Under the ordinance, the district has implemented various CPTED projects, and even received the grand prize in the 2017 Korea Crime Prevention Awards for its systematic and efficient efforts.

The target area of Project B implemented by District A in 2016 is largely comprised of single-person households in multiplex housing, and shows high homogeneity in physical environment across areas. Most buildings are less than five stories high, and sidewalks are not separated from roads. Visibility is limited by the narrow streets and alleys between buildings. The area had a high proportion of residential burglary and violence before the implementation of Project B. The residents have a high fear of crime, but are less aware of crime prevention methods.

This study selected a target area where the CPTED project had been implemented in a residential area, allowing analysis of effects before and after the project, and where crimes had occurred to an extent such t