The Evidence on Displacement

Universal assertions that displacement inevitably occurs in the aftermath of problem-led policing efforts are largely based on unfounded suppositions rather than empirical facts.7 Research has consistently found that crime displacement is the exception rather than the rule and that diffusion of benefits is just as likely and sometimes more likely to occur. In cases where some displacement occurs it tends to be less than the gains achieved by the response. Familiarizing yourself with this research allows you to justify your efforts to potential critics particularly during the early stages of your project before you've assessed displacement and diffusion effects of your own.

One of the most comprehensive reviews of the extent of displacement among evaluations of situational-focused crime prevention projects, conducted in 2008 by Guerette and Bowers, found that displacement and diffusion are equally likely to occur. Table 1 presents some of the results from this analysis (See Appendix A for more information). Displacement tends be observed in 26 percent of the instances where it is examined, and diffusion is observed 27 percent of the time. This research also suggests that of the different types, temporal displacement is most common (occurring 36 percent of the time), followed by target (33 percent), offense (26 percent), spatial (23 percent), and tactical (22 percent). As for diffusion, spatial diffusion seems to be most common (occurring 37 percent of the time) followed by target (24 percent), offense and temporal (each at 16 percent), and tactical (12 percent).

Table 1: The Extent of Displacement and Diffusion by Type8
Study N = 102		Displacement	Diffusion of Benefit
Type	Examinations Frequency (%)†	Observed Frequency (%)††	Observed Frequency (%)
Spatial	272 (47%)	62 (23%)	100 (37%)
Offense	140 (24%)	36 (26%)	22(16%)
Target	80 (14%)	26 (33%)	19 (24%)
Tactical	49 (9%)	11 (22%)	6 (12%)
Temporal	31 (5%)	11 (36%)	5 (16%)
Total	572†††	146 (26%)	152 (27%)

Source: Guerette and Bowers (2009).

† Column percentages are reported (e.g., percent of the overall number of inspections (n = 572).

†† Row percents are reported (e.g., percent of those inspections of specific displacement/diffusion type).

††† Does not equal the number of studies in the review (i.e. 102) since several studies examined multiple forms and multiple inspections of displacement/diffusion.

An analysis of a subsample of 13 studies, which allowed for the assessment of the prevention project's overall outcomes while accounting for spatial displacement and diffusion effects, found that when spatial displacement did occur, it tended to be less than the response effect, meaning that, on average, the responses were still beneficial.9 Previous reviews of crime prevention evaluations also found that the extent of displacement is usually limited.†

† Specifically, of the 33 studies reviewed by Eck (1993), 91 percent found no or little displacement (e.g., displacement less than the response gain) and only three (9 percent) reported a substantial amount. Similarly, Hesseling (1994) found that 40 percent of the 55 studies reviewed reported no displacement at all, and, of these, six reported diffusion of benefits.

Research also shows that displacement is unlikely in the aftermath of broader community development programs10 and more focused policing initiatives that centered on hot spots.11 An evaluation of the Weed and Seed program in Miami, Florida, found that spatial diffusion of benefits occurred more commonly than spatial displacement.12 An evaluation of the New Deal for Communities (NDC) program in the United Kingdom discovered that, among 383 buffer zones, spatial diffusion of benefits was observed in 23 percent of zones, while spatial displacement was observed in only 2 percent. The remaining 75 percent showed no signs of displacement or diffusion. Also, across the buffer zones offense diffusion was more common than offense displacement (between 21 and 25 percent of the zones revealed offense diffusion compared to 0 to 5 percent for offense displacement).13

A systematic review of the effects of hot spots policing on crime found that of the five studies that examined displacement and diffusion effects none reported "substantial immediate spatial displacement of crime into areas surrounding the targeted locations" while four suggested possible diffusion effects.14 A randomized experiment testing for the presence of displacement in a problem-oriented policing project in Lowell, Massachusetts, found no significant displacement to the areas immediately surrounding the targeted places.15

It should be noted, however, that there may be times when displacement is simply undetectable. Offenders may move to other jurisdictions from which no data can be obtained, they may switch to offenses that are more difficult to detect (such as Internet fraud), or they may switch to offenses that have a very low reporting rate (such as shoplifting). Because of this, the research findings reported above may undercount the true extent of displacement effects. Nonetheless, the collective message of this research is that displacement is much less of a problem than originally and commonly believed.

When and Where Displacement May Occur

Whether displacement occurs is largely determined by three factors: offender motivation, offender familiarity, and crime opportunity. Offender motivation determines which offenders and types of crimes are likely to be displaced. Offenders driven by drug addiction are more likely to displace their crime behavior to crime types and targets that facilitate their addiction16 just as career criminals are more likely than marginal (opportunistic) offenders to continue to engage in crime after a response because their motivation is greater. Likewise, instrumental offenders (i.e., those motivated by monetary gain) are more likely to seek out other crime targets and types that provide similar monetary gain.17 Differently, motivations of expressive offenders (those motivated by emotion) tend to be contextually dependant. Expressive offenders are also less likely to displace their behavior once their situation is altered or otherwise remedied. Motivation is, however, influenced by offenders' familiarity with other locations and tactics and the prevalence of crime opportunities in their knowledge area.

Offenders are more likely to relocate their behavior to crime targets, places, times, and tactics with which they are most familiar.18 This means if displacement occurs it is most likely to be close to the original crime location and involve similar targets† and tactics. Termed "familiarity decay," for spatial displacement this means the probability of displacement is greatest close to the original crime location and decreases as the distance from the response area increases (see Figure 1). Offenders are less likely to offend in unfamiliar locations because it poses greater risk and greater effort to familiarize themselves with new locations. Distance from the original crime location increases the probability of unfamiliarity among offenders.

† Similar meaning that the new offenses will involve targets and crimes that provide 'similar' rewards for the offender.

Displacement to the area immediately surrounding a response area is particularly likely if the crime area targeted by the intervention is a crime attractor,† a place to which offenders travel to commit crime because they present known crime opportunities (e.g., shopping malls, entertainment districts, or drug and prostitution areas). This provides minimal effort for offenders while also allowing them to operate within their zone of familiarity. Familiarity with locations also provides lower risks for offenders because they can more readily identify entry and exit points that will allow them to approach and leave crime scenes more quickly. Offenders' spatial familiarity is primarily determined by the known places and the surrounding vicinity that they frequent as part of their normal living routines. These areas of familiarity include the:

• place(s) they currently or previously worked, if employed;
• areas near their current or previous residence;
• areas near where they participate in activities and/or shop;
• areas near the residence of significant others, such as friends or family members; and
• routes they travel going to and from each of these places.

† For more on crime attractors, see steps 17 and 28 of Clarke and Eck's (2005), Crime Analysis for Problem Solvers in 60 Small Steps.

For target and tactical displacement, familiarity means offenders are more likely to select similar targets and use tactics similar to those they have used in former crimes. The more dissimilar other targets and tactics needed to commit other crimes; the lower the probability offenders will engage in them, at least in the near term. Most offenders acquire skill sets from peer groups or other delinquent associations as well as through their direct and indirect experiences of committing crime.20 In the absence of other available crime targets (or at least those that the offender(s) is aware of) that provide for the use of existing skill sets, displacement is much less likely. Highly motivated offenders may expend the effort to acquire new skill sets, but the more common opportunistic offender is less likely to do so.

Table 2: Predictors and Factors of Displacement
Predictors	Factors	How it relates to displacement
Offender Motivation	Addiction High Motivation (career offenders) Low Motivation (opportunistic offenders) Instrumental (motivated by money)† Expressive (usually violent or destructive)	Likely to displace to other crimes that facilitate addiction. More likely to displace than desist from crime. More likely to expend the effort to find new crime opportunities and/or learn new skills. More likely to desist from crime than displace. Less likely to expend the effort to find new crime opportunities and/or learn new skills. More likely to seek out other crime targets and types that provide similar monetary gain. Usually highly contextual. Less likely to displace once situation is altered or remedied.
Offender Familiarity of other targets/locations/skill sets	High/many Low/few	More likely to displace crime behavior. Less likely to displace or will take longer to do so.
Crime Opportunity	Nearby Distant	More likely to displace crime behavior. Less likely to displace or will take longer to do so.

† Instrumental motivations may be violent, but the purpose of the violence is to secure monetary gain. Examples of this would include violence used during robbery, or by drug dealers to collect payments or to deter other drug dealers from operating in their turf zones.

The presence of crime opportunities also determines when and where displacement occurs. For many of the reasons already discussed, displacement is more likely where there are other suitable crime targets. This is contingent upon the offenders' motivation and familiarity with the crime targets and tactics needed to carry out the crime. Responses that occur adjacent to areas that have unprotected crime targets are more likely to experience some level of displacement compared to those that do not. Being aware of other crime opportunities near your response area allows you to anticipate the possibility of crime movement.

Why Displacement May Not Occur

Some criminality theories suggest that displacement inevitably occurs because crime behavior is the product of societal forces outside the individual, which instill criminal predispositions, or drives, within offenders. Because of the assumed need for offenders to "purge" their criminal tendencies or sustain certain income levels from criminal enterprises, this view contends that blocking crime opportunities through situational alterations inevitably compels offenders to seek out other crime opportunities (e.g., displacement occurs). Yet, this displacement assumption fails to recognize the important role that opportunity and temptation play in crime.

Offenders displace their criminal behavior only when the risks and effort of committing new crimes are worth the reward.21 Because different crimes present different costs, efforts, and rewards, there are many instances when displacing crime behavior is not worthwhile for the offender. In other words, opportunities to commit crime are not evenly distributed across time and place. Another aspect to consider is that when crime opportunities are closed down, committing other crimes is not the only way offenders can meet their needs. Blocking crime opportunities can make satisfying individual needs through legitimate activities more appealing.

Consider the following examples. It is unlikely a casual shoplifter would travel to a distant supermarket when newly introduced security makes it impossible for him to steal the odd item at his local market. It is also unlikely that commuters would seek another, less convenient route to work if it became impossible for them to exceed the speed limit on their current route. It is also implausible that travelers who casually take hotel items would expend the effort to seek out hotels that did not secure their alarm clocks, wall pictures, or closet hangers. Finally, when a store well known for selling alcohol to underage drinkers is shut down or otherwise brought into compliance, it is doubtful underage drinkers will simply go down the road to the next vendor because most vendors do not distribute to minors and the youth may not know which other ones do.

Put simply, very easy opportunities encourage crime and taking them out reduces the amount of crime committed. An offender's decision as to whether to displace his crime behavior in the aftermath of a response is shaped by the variety of circumstances found among other crime types, targets, times, tactics, and places.22 This means displacement often does not occur because:

• Offenders' knowledge is bounded in terms of knowing how to commit various types of crime (e.g., the tactics involved; skill sets).
• Offenders are less likely to commit crimes in unfamiliar locations or that involve unfamiliar tactics and targets.
• When blocked from their usual means of committing crime, even highly motivated offenders have to take time to scout out new territories and/or learn new ways to commit offenses. This means less crime, at least in the near term.
• Some offenders have a limited amount of time to commit crime.
• Illicit markets (such as street drug and prostitution) are often informally governed by competing offenders, which discourages displacement of outsiders into protected turf zones.

These crime features also explain why diffusion of benefits occurs. Two processes relate to diffusion: deterrence and discouragement.23 As a prevention program in one area becomes known, offenders' uncertainty about the extent of the increased risk (deterrence) is coupled with the exaggerated perception that the rewards of particular crimes are no longer proportionate with the effort (discouragement). Thus, diffusion is likely to occur in places near response areas.