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Introduction
In their classification of situational crime prevention, Cornish and Clarke (2003) differentiate three types of surveillance that are used to prevent crime in public places: formal surveillance, natural surveillance and place managers (or surveillance by employees).1 In the parlance of situational crime prevention, each is aimed primarily at increasing offenders' perceived risks of committing a crime. Formal surveillance aims to produce a 'deterrent threat to potential offenders' (Clarke 1997a, p. 20) through the deployment of personnel whose primary responsibility is security (for example, security guards) or through the introduction of some form of technology, such as closed-circuit television (CCTV) cameras, to enhance or take the place of security personnel. Place managers (Eck, 1995) are persons such as bus drivers, parking lot attendants, train conductors and others who perform a surveillance function by virtue of their position of employment. Unlike security personnel, however, the task of surveillance for these employees is secondary to their other job duties.
Natural surveillance shares the same aim as formal surveillance, but involves efforts to 'capitalize upon the 'natural' surveillance provided by people going about their everyday business' (Clarke, 1997a, p. 21). Examples of natural surveillance include the installation or improvement of street lighting and defensible space (Newman, 1972). The latter involves changes to the built environment, as well as more mundane techniques such as the removal of objects from shelves or windows of convenience stores that obscure lines of sight in the store and the removal or pruning of bushes in front of homes so that residents may have a clear view of the outside world.
CCTV and improved street lighting are the most well developed surveillance measures that are in current use. This is true at least in terms of the body of work that has been carried out over the years to evaluate these measures. In our updated systematic reviews of these two interventions, we obtained and analyzed a total of 57 evaluations of high methodological quality (that is, involving before-and-after measures of crime in experimental and mostly comparable control areas); another 66 less rigorous evaluations were also obtained and analyzed (Farrington and Welsh, 2007; Welsh and Farrington, 2009) for our earlier reviews, see Farrington and Welsh, 2002; Welsh and Farrington, 2004). And in recent years,...