of Philadelphia, 2012). CCTV systems have the potential to aid crime investigations, identify
offenders, streamline police response, increase punishment certainty, and reduce the public fear
of crime (Ashby, 2017; LaVigne et al., 2011; Piza, Caplan, & Kennedy, 2014; Ratcliffe, 2006).
When police have been proactively tasked based on activity observed by CCTV cameras, significant
reductions in violence and social disorder have been observed (Piza, Caplan, Kennedy, & Gilchrist,
Studies of urban public CCTV systems are increasing, though at the time of Welsh and Farring-
ton’s (2007) systematic review, they identified only 22 from 44 studies that were applicable to city
centers and urban public areas, and their conclusions were dominated by the results from public car
parks. The earliest independent evaluation of a CCTV implementation dates from King’s Lynn, UK
(Brown, 1995), where 19 cameras were installed at public car parks across the city; however like
many studies that followed, this evaluation suffered methodological issues such as a lack of controls
for low numbers of initial crimes and for long-term temporal trends. Overall, the existing CCTV
evaluation literature displays considerable variation in n ot only methodology but also outcome
measures and independent variables. Some studies examined the impact of cameras on crime within
a defined distance of CCTV cameras (Harada et al., 2004), while others surveyed residents in camera
areas for their perceptions of how crime has changed (Squires, 2003). Other studies have interviewed
key stakeholders (Hood, 2003) or examined emergency room attendance levels related to assaults
after the introduction of a CCTV surveillance system (Sivarajasingam, Shepherd, & Matthews,
2003). To date, few researchers have addressed the challe nge represented by camera viewshed
overlap that has theoretical and—more importantly—analytical implications (Lim & Wilcox,
2017, is a recent exception). Cameras in close proximity to each other with overlapping viewsheds
may not necessarily work independent of each other; instead their effect may be enhanced by the
presence of multiple cameras magnifying the deterrence signal to potential offenders.
This article reports the results of a quasi-experimental, longitudinal study of the violence and
disorder impact of 13 clusters of CCTV cameras (86 cameras in total) in the city of Philadelphia, PA.
After a brief overview of the theoretical rationales for CCTV implementation, the article describes
the methods, camera design, study setting, and the analytic approach. We report the results for two
crime types and summarize the findings before discussing them and offering implications.
CCTV cameras may reduce crime in a number of ways. Drawing on a rational choice and situational
crime prevention framework (Clarke & Felson, 1993; Cornish & Clarke, 1986), the prevention
mechanism most commonly argued is deterrence through a potential offender becoming aware of
a camera and deciding that the risk of their identity being captured outweighs the benefits of the
imminent offense (LaVigne et al., 2011; Piza et al., 2015; Ratcliffe, 2006). Within a situational
framework, CCTV camera schemes fall under the general approach of increasing the risks of
committing crime and represent a “formal surveillance” technique that enhances or replaces the
role of security staff or the police (Clarke & Eck, 2005; Welsh & Farrington, 2008).
In one study, police actively monitored the CCTV with the explicit intention of anticipating
trouble in a popular bar area of the town of Malm}
o, Sweden. When the camera monitor observed an
incipient disturbance, officers were dispatched to the scene to de-escalate situ ations or prevent
ongoing fights escalating (Gerell, 2016). Within the situational crime prevention framework, this
combination of technology and organizational response would seek to reduce provocations. How-
ever, most researchers hypothesize the primary mechanism is offender awareness of camera location
and that awareness will generate a change in the perception of risk and subsequently a reduction in
offending (Piza et al., 2015).
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