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Foot patrol, hotshots, randomized trial, deterrence, violence, public health Originating with the Newark, NJ, foot patrol experiment, research has found police foot patrols improve community perception of the police and reduce fear of crime, but they are generally unable to reduce the incidence of crime. Previous tests of foot patrol have, however, suffered from statistical and measurement issues and have not fully explored the potential dynamics of deterrence within microscopically settings.
In this article, we report on the efforts of more than 200 foot patrol officers during the summer of 2009 in Philadelphia. Geographic information systems (GIS) analysis was the basis for randomized controlled trial of police effectiveness across 60 violent crime hotshots. The results identified a significant reduction in the level of treatment area violent crime after 12 weeks. A linear regression model with separate slopes fitted for treatment and control groups clarified the relationship even more.
Even after accounting for natural regression to the mean, target areas in the top 40 percent on pretreatment violent crime counts had significantly less violent crime during the operational period. Target areas outperformed the control sites by 23 percent, resulting in a total et effect (once displacement was considered) of 53 violent crimes prevented. The results suggest that targeted foot patrols in violent crime hotshots can significantly reduce violent crime levels as long as a threshold level Of violence exists initially.
The findings contribute to a growing body of evidence on the contribution of hotshots and place-based policing to the reduction of crime, and especially violent crime, which is a significant public health threat in the United States. We suggest that intensive foot patrol efforts in violent hotshots may achieve deterrence at a microscopically level, primarily by increasing the retainer of disruption, apprehension, and arrest. The theoretical and practical implications for violence reduction are discussed. For most of the history of American policing, the role of foot patrols in public safety has been almost mythical.
The growth of the night and rattle watches of the 1 sass was the consequence of the assumed deterrence abilities of a patrolling, uniformed authority carrying the explicit threat of government intervention should social order unravel. To this day, we have a consistent public demand for foot patrols as a “proactive, non-threatening, community- oriented approach to local policing’ (Wakefield, 2007: 343). Key questions yet remain. For example, do foot patrols achieve more than simply providing reassurance to the public?
Does the enhanced visibility of officers on foot, instead of in cars, serve a significant and measurable deterrent effect? The evidence to date on these questions has been mixed, PHILADELPHIA FOOT PATROL EXPERIMENT 797 despite that the police have long been assumed to provide a deterrence function. This assumption can be traced back to the writings of both Beneath (1948 [1789]) and Bacteria (1 963 [1764]) who argued for the need to influence he calculus of would-be criminals, for society to ensure that the costs of committing a crime would be outweighed by any potential benefits.
Bacteria argued that the central mechanisms for adjusting this calculus are certainty of detection, severity of punishment, and celerity (or swiftness of punishment) (see Angina and Pockmarks, 2001 The very origins of the police institution rest on this view. Sir Robert Peel established his police in London, U. K. , as a means of providing an “unremitting watch” (Shearing, 1996: 74) through visible patrol. Citizens would be deterred through this system of surveillance, knowing that their chances of being caught and punished would be high.
Yet, despite the longevity of the deterrence doctrine, the evidence on whether the practice of foot patrol actually deters crime has been weak. Following the Kansas City preventative patrol experiment finding that vehicle-based patrol had no significant impact on crime rates (Keeling et al. , 1974), the Newark foot patrol experiment did much to cement the view among many criminologists that varying the dosage of uniformed patrol has no quantifiable impact on crime (Keeling, 1981).
Varying foot patrol levels across 12 Newark, NJ, beats exulted in no significant differences between treatment and control beats for recorded crime or arrest rates, although treatment areas did show improvements in community fear of crime (Pate, 1986). Additional studies followed, ranging in magnitude and scope. For example, four foot patrol officers in a business district of Asheville, NC, had the same, apparently negligible, impact on recorded crime as the 300 officers moved to foot patrol as part of the Boston Police Department’s 1983 Patrol Reallocation Plan (Bowers and Hirsch, 1987; Suspense, 1987).
Notwithstanding this lack of evidence, foot patrol became “the most popular and widely implemented component of community policing’ (Rosenberg and Luring, 1994: 303) even if many police departments adopted foot beats more to address community relations and fear of crime than for any direct crime deterrence benefits (Coroner, 1986; Jim, Mitchell, and Kent, 2006). The National Research Council (2004) review of police policy and practices summarized foot patrol as an unfocused community policing strategy with only weak-to-moderate evidence of effectiveness in reducing fear of crime.
Since these early foot patrol studies, criminologists have gained a more nuanced understanding of criminal behavior within spatial and temporal contexts. For instance, both routine activity theory (Felon, 1987) and crime pattern theory (Birmingham and Birmingham, 1984) identify place as a fundamental component of the requirements of a crime, the centrality of 798 which environmental criminologists have adopted as a potential avenue along which to promote crime-control opportunities. It is now widely understood that crime clusters within highly specific geographic locations, commonly termed “hotshots. L A crime hotshot is the accepted term for what was originally described as a cluster of addresses (Sherman and Whispered, 1 995), widened to include the possibility of street intersections and public space (Burger, Cohn, and Petitions, 1995). The term is now generally defined as a “geographical area of higher than average crime . An area of crime concentration, relative to the distribution of crime across the whole region of interest’ (Chained and Radcliff, 2005: 145-6). With the growth of crime mapping, crime hotshots have become significant loci for focused police activity.
With a refocusing on place, location-specific crime prevention can add to neural offender deterrence with options to prevent potential offenders from committing crime at a specific location. Angina (2010: 313) recently pointed out that effective deterrence stems from a tangible and direct prospect of detection, and that focused policing at crime hotshots “is probably effective because it tangibly and directly increases apprehension risk at the hot spot by substantially increasing police presence. Although the National Research Council’s (2004) review lamented the paucity of quality studies on the benefit of proactive police activity such as field interrogations and traffic enforcement, we have long had general support from Wilson and Bollard’s (1978) study of 35 cities to suggest that even some unfocused proactive police activity can have a reductive effect on robbery.
A more extensive study of 171 American cities and the proactive drink/drive and disorder activities of police again found a similar dampening effect on robbery (Sampson and Cohen, 1988), and a recent update with a more fully specified statistical model again found a significant negative association between robbery rates and proactive policing across a similar number of U. S. Cities (Kabuki et al 2010).
Focusing on gun violence, studies including the Kansas City gun intervention (Sherman, Shaw, and Organ, 1 995) and the Indianapolis directed patrol project (Mackerel, Charmer, and Weiss, 2002) led Keeper and Mayo- Wilson (2006) to conclude that directed patrols targeted to the carrying of illegal weapons had a suppressive effect on gun violence at high-risk places and times. 2. The research and professional literature refers to both “hotshots” and “hot spots. ” We use the former throughout simply for the purposes of consistency.
This is defined broadly in this context as police activity that is not reactive to alls for service from the public but indicative of a police decision to take action where such activity could be considered discretionary, for example, to initiate a traffic stop for a minor traffic violation, to conduct a field interview, or to undertake surveillance of a known offender. 799 A strong evidence base has similarly emerged in relation to the positive effects of the related strategy, hotshots policing.
Echoing the findings of previous studies (such as Brag and Bond, 2008; Sherman, Gratin, and Burger, 1 989; Whispered and Brag, 2006), both the National Research Council (2004) and Brass’s (2007) systematic review concluded that focused hotshots policing works. Previous hotshots experiments have to date examined problem-oriented policing rather than foot patrol per SE (Brag et 1999), or where foot patrol strategies were mixed with other interventions such as vehicle patrols (Sherman and Whispered, 1995; Whispered and Green, 1995).
A rare exception is the British study in Hull, Humidifiers, where additional foot patrols in the city center reduced personal robbery during the course of a year by 16 percent while regional and national rates increased (Jones and Tillie, 2004). Given this new evidence, we suggest it is timely to reexamine the question of whether foot patrol, as a specific hotshots intervention, holds promise as an approach to reducing crime, and especially violent crime, which is a leading cause of death and injury in the United States (see Miller, Cohen, and Oarsman, 1993).
In light of the theoretical advances discussed, and the development of new techniques in spatial analysis, one can revisit the research designs of earlier foot patrol studies with fresh eyes. Sherman and Whispered (1995) already have pointed out that many of these early studies suffered from statistical ND measurement problems, namely, a statistical bias across rephrased studies toward the null hypothesis, and the measurement issue of an often inappropriate study area.
The latter problem addresses the question of whether to organize a project by police districts, police beats, or other areas. Even if hotshots policing was part of the lexicon at the time, the ability to achieve a microscopically focus traditionally has been hampered by the need to measure and organize police resources by larger administrative regions.
This issue has to some extent been resolved with the development of geographic information systems (GIS) and the accompanying field of geographic information science (Gigs), although as Renter and Lockwood (2009: 110) pointed out, many crime analysts simply accept the “bounded space that is available to them rather than construct their own boundaries. ” GIS and GIGS together provide both a tool and an analytical regime to approach spatially customized target areas for crime prevention activities.
Thus, more recent police effectiveness research projects have been able to concentrate on crime hotshots. The ability over time to move down through the cone of resolution Birmingham, Dryness, and Birmingham, 1 976) from studying large administrative areas to smaller and smaller spatial units has enabled crime researchers to now explore crime hotshots at micro units of place, which are defined as addresses, street segments, or clusters of these microscopically units 800 (Whispered, Verbenas, and Bruins, 2009:4).
A focus on smaller places can address dosage concerns; concerns that foot patrol officers assigned to replace vehicle-based patrol in large geographic areas will be spread too thin, thereby diminishing any deterrence effect that could have been created by heir presence. Spatially oriented crime-control programs have actively addressed the redecoration of places that provide crime opportunities, looking to a location focus to create constraints on criminality.
Whispered and Green (1995: 731 ) employed a randomized control design to examine a 7-month operation to reduce drug activity at drug hotshots in Jersey City, NJ, and found “consistent, strong effects of the experimental strategy on disorder-related emergency calls for service. ” Taking the cone of resolution to individual properties and corners, Green (1995) found an Oakland, CA, program that embodied traditional enforcement with third-party interventions targeted at nuisance drug locations not only reduced drug problems but also demonstrated a diffusion of benefits to nearby locations.
The potential diffusion impact of crime prevention strategies at specific locations raises the question of how interventions such as foot patrols can prevent crime. General and specific deterrence may occur if the presence of a police officer is sufficient to increase an offender’s perceived risk of apprehension (Angina, 2010). A second potential mechanism is “proactive policing’ (Kabuki et al. 01 0), whereby the activity of a police officer, such as stopping and questioning suspects, performing a stop-and-frisk (also known as a Terry stop), or (with probable cause) conducting a full search of a suspect, may increase the chances that police will identify a fugitive or find illegal weapons or items and increase the arrest rate. The visible enforcement of minor infractions and disorder offenses may be perceived by offenders as indicative of a change in the apprehension risk, according to Sampson and Cohen (1988).
Therefore, deterrence can potentially occur through officer presence, r where specific activities of police officers either increase the arrest-offense ratio or the perception that it has increased (Kabuki et al. , 2010). Spatial diffusion of benefits may occur if offenders perceive that officers patrolling a nearby hotshot may be able to intervene quickly should the alarm be raised about a crime, or if patrol boundaries are not known to offenders.
A spatial diffusion could also occur if deterrence can serve to discourage the carrying of crime-enabling items, a change that can affect the offender both inside and outside the target area. Conversely, place-based interventions can theoretically displace crime to repay areas if officers never patrol nearby areas, and if the boundaries of the target area are known to local offenders. Yet even in these scenarios, displacement may be beneficial.
Offenders may move to spaces that are less inviting or less familiar to them, resulting in a reduction of their activity. 801 Specific behaviors like drug market activity could be displaced to less public spaces, away from children, recovering drug addicts, and everyday people such that these groups are less exposed to the harms associated with dealing and selling (Caulking and Reuters, 2009).
The social harm outcomes of reactive police activity can therefore be theoretically beneficial in either a diffusion or a displacement regime. Displacement can move criminal activity to less optimal (Attaining, Renter, and McCoy, 2009) or less public locations, whereas a diffusion of benefits could mean reduced exposure to violence overall, which is a crime reduction outcome that also has been associated with improved public health outcomes (Guard, Houseman, and spindled, 2003).
At the outset we should note that disentangling specific deterrence effects of officer presence versus officer (proactive) activity are beyond the reach of this duty; however, within the broad research literature outlined earlier, our current study of officers walking patrol areas concentrated at crime hotshots can be characterized as a study of both foot patrol as well as hotshots policing. The remainder of this article reports on what the authors believe is the first large-scale, randomized controlled experiment of the effectiveness of foot patrol to reduce violence in crime hotshots.
EXPERIMENTAL DESIGN BACKGROUND TO THE PHILADELPHIA EXPERIMENT Philadelphia is the fourth largest police department in America, with more than 6,600 police officers. These officers police a city of nearly 1. 5 million people, recently ranked the 30th most dangerous in the United States (Morgan, Morgan, and Boob, 2010). Violence, recognized as one of the worst public health threats both nationally and locally (Centers for Disease Control and Prevention, 201 0), remains a problem in the city.
In 2008 (the year before this study intervention), 331 homicides took place in the city, and since the year 2002, Philadelphia has experienced more than 100 shootings per month (Radcliff and Renter, 2008). Although the city had witnessed a gradual reduction in violent crime levels for couple of years, a noticeable and consistent seasonal cycle of increases in violent crime has been occurring during the summer months (figure 1).
A pilot study of 43 foot beats patrolled during the summer of 2008 indicated a modest reduction in violence in the target areas, with a slight diffusion of benefits to a buffer area of approximately 1 ,OHO feet around target sites (Radcliff and Attaining, 2008). With the availability of two waves of new recruits emerging from the police academy in March and late June 2009, we were provided with an opportunity to conduct a larger study. Police Commissioner Charles Ramsey 802 Figure 1 .
Weekly Violent Crime Counts, 2006 to October 2009, Philadelphia, PA expressed a desire to focus the new recruits emerging from the police academy toward small, targeted foot patrols in high violent crime areas primarily to reduce summer violent crime. SELECTION OF RANDOM ASSIGNMENT HOTSHOTS We followed a multiples process to identify the most dangerous places in Philadelphia. During January and February 2009, violent crime reports were drawn from the incident (INC) database of the Philadelphia Police Department for 2006, 2007, and 2008. Violent crime was defined as homicide, aggravated assault, and robberies not occurring indoors (the outdoor selection of offenses being in line with the approach of Sherman and Whispered, 1995). These categories of serious violent crime are typically not affected by issues with crime reporting or police discretion (Gave, Hughes, and Green, 1985). Crime events were weighted so events from 2008 counted 1. 00, 2007 crimes counted . 50, and 2006 crime events counted . 25.
In this way, more recent events had greater relevance in the creation of the target locations for 2009, but the area values could retain a portion Of the long-term hotshot component, given many urban locations have long-term rime trajectories (Whispered et al 2004). These weighted values were summed for homicide, aggravated assault, and robbery, and then these events were mapped and aggregated to spatial units called Thistles 3. We recognize that other studies have relied exclusively on calls for service or some combination of calls for service and reported crime.
However, in busy metropolitan police departments, the calls for service files are prohibitively large and not routinely used to inform patrol. District and regional commanders in Philadelphia are accountable to the number of crime incidents rather than to the frequency Of calls for service. 03 polygons to create a Version network of spatial units. A Version network consists of real units created by using lines to divide a plane into areas closest to each of a set of points (in our case, street intersections) such that the space within each polygon is closer to the specific point within than to any other point (Chairman, 2002).
For points, we chose the nearly 22,000 intersections in the city. The Version network as a unit of analysis is very similar to the “epicenter” (Sherman and Whispered, 1 995) and “intersection area” approaches (Brag et al. , 1999; Whispered and Green, 1995) used in revises place-based experiments. Those experiments either included the entire blocks associated with an intersection (Brag et al. , 1999; Whispered and Green, 1995) or a more subjective measure of “as far as the eye could see from sidewalk corners” in each direction (Sherman and Whispered, 1995: 633).
Polygons greater than one million square feet were excluded,4 and a map of weighted violent crime totals for each polygon were presented to the two Philadelphia Regional Operations Commanders (ROCK North and ROCK South), with the top 220 violent crime corner polygons highlighted. This top 1 percent f corners (approximately, based on the 3-year weighted values) contained 15 percent of the 2008 robberies, 13 percent of 2008 aggravated assaults, and more than 10 percent of all 2008 homicides.
The top 5 percent of corners accounted in 2008 for 39 percent of robberies, 42 percent of aggravated assaults, and 33 percent of homicides. Police commanders informed us that they would have sufficient personnel to cover 60 foot patrols for 16 hours a day, 5 days a week, so the ROCs were asked to identify at least 1 20 potential foot patrol areas of roughly equivalent size, where each patrol area must contain at least 1 of the top 220 violent rime corners in the city. TO aid the creation of patrol areas, We mapped the results of a local Moron’s spatial autocorrelation test (Angelina, 1995; Moran, 1950).
Local Moron’s is one of a range of local indicators of spatial association (LISA) statistics available to crime scientists that can indicate clustering of high crime values (Angelina, 1996; Get’s and Rod, 1992, 1996; Union, 1996). Mapping polygons with high violence counts that were among high violence neighbors enabled police commanders to see where the hottest corners were surrounded by other high crime areas and, from this information, to construct more effective foot patrol areas.