Crime Prevention through Environmental Design (CPTED) refers to measures taken to reduce crime through the manipulation of the physical environment. CPTED outlines a set of principles designed to influence potential offenders' perceptions of the risk, effort and rewards of offending.
This review covers the application of CPTED to prevent commercial robberies in retail settings. These could be implemented with single or multiple components. Single components included implementing cash handling procedures, adding a second clerk during night-time business hours, hiring guards, or installing security hardware systems (e.g., alarms, video cameras, CCTV). Multiple components generally packaged together low- to no-cost recommendations such as keeping a minimum amount of cash in the register, maintaining good visibility and lighting into and out of the business, limiting access and escape routes and training employees in how to respond to a robbery. The last type of intervention were those mandated by ordinances – local by-laws common in US states – which require a combination of measures outlined above.
This narrative is primarily based on one systematic review covering 26 studies.
Overall, evidence suggests that CPTED has no impact on robbery (but some studies suggest a decrease in commercial robberies in retail settings). This finding requires careful consideration given the age of the reviewed studies and the low quality of supporting evidence.
The majority of studies reviewed experienced a percentage reduction in robberies, though two studies showed an increase in commercial robbery. For these latter two, whilst the increases experienced were noteworthy (by 212.5% and 130%), these findings are not statistically reliable (due to weak research design and no reporting of statistical significance).
Differences in the outcome measures used across the evaluations prevented the calculation of an overall effect size. However an average reduction in robbery of 30% was observed across studies with a comparable area or time period (16 studies). The review did not report the statistical significance of changes in robbery. Among studies examining the monetary loss per robbery, businesses with the intervention lost on average 9.5% less in dollars than the control group.
Although the review was systematic, many forms of bias that could influence the study conclusions remain. This evidence is taken from a systematic review covering 26 (US based) studies. However, these studies were all pre-2000 and were mainly assessed to be of poor design. Only one randomised experimental study and one quasi-experimental study was available for inclusion in this review. The quasi-experimental study was rated as rigorous; the randomised experimental study did not fully control for biases in the selection process. The quality of other studies was limited by combinations of factors including: the absence of suitable comparison groups, the absence of pre and post comparisons and the use of crude or inappropriate outcome measures. This means that the evidence of effect is weak.
The review does not explain or test the mechanisms through which CPTED might reduce robbery.
The review did not test for variations in CPTED effectiveness in different retail outlets although it did distinguish between multiple and single component programmes and ‘ordinances’ (requirements by State laws). Multiple component programmes appear to have been more effective, with all programmes experiencing reductions in robberies in relation to a comparison group and/or time period (reductions ranged from 30% to 84%). The findings of evaluations of single component programmes and ‘ordinances’ reveal mixed results, with single-component program effects ranging from reductions in robberies of 83% to increases of 91%, and the effect of ordinances ranging from reductions of 65% to increases of 130%.
The review noted that reductions in robbery were associated with employing a second clerk (2 studies), installing security hardware systems (4 studies), hiring guards (1 study) and improving cash handling procedures (1 study).
No details on implementation were provided; although the degree to which programmes followed the implementation plans was often low. Average compliance (with implementation plans) was less than 30% (6 studies). The review suggests that lower-cost CPTED changes tend to result in higher compliance, however this was not tested.
In three of the five studies evaluating the introduction of new equipment, the functioning of the equipment was not monitored. Overall, the review highlights that implementation failure could have affected the results observed.
The review does not mention costs (and/or benefits) and no formal economic analysis is provided.
The authors note that the evaluations included in the reviews varied in important ways, including the outcome measures used.
Displacement of crime or diffusion of benefits to neighbouring areas or businesses was not reported, but should be considered a possibility.
Compliance with the CPTED interventions was often low. When serious, this could have led to implementation failure, therefore undermining the true effect of the intervention.
Cost information for CPTED is difficult to determine. As technologies change costs can increase or decrease, and costs will vary by location and the characteristics of business premises.
This review has highlighted substantial gaps in the evidence base, specifically the need for more robust studies utilising experimental or quasi experimental designs, the need to directly test the underlying mechanisms and the need to explore variations in effectiveness by context.
Overall, evidence suggests that CPTED has no impact on robbery (but some studies suggest a decrease in commercial robberies in retail settings). The evidence, however, is old and of low quality. No information was provided on the effectiveness of CPTED as a means of reducing retail robbery in different kinds of premises.
Review: Casteel, Carri and Peek-Asa, Corrine (2000) 'Effectiveness of Crime Prevention Through Environmental Design (CPTED) in Reducing Robberies', American Journal of Preventive Medicine, 18:4S, 99-115
This narrative was prepared by UCL Jill Dando Institute and was co-funded by the College of Policing and the Economic and Social Research Council (ESRC). ESRC Grant title: 'University Consortium for Evidence-Based Crime Reduction'. Grant Ref: ES/L007223/1.
Uploaded on 19/02/15