Disorder policing to reduce crime: A systematic review

Policing social and physical disorderly conditions is rooted in the broken windows approach: disorder is a precursor to more serious crime, fear of crime, and neighborhood decline. Addressing disorder has become a central fixture of policing, especially in the United States. Yet, evaluations of the effectiveness of disorder policing strategies in controlling crime yield conflicting results. Policing disorderly conditions can be divided into two main strategies: (a) order maintenance or zero tolerance policing, where police attempt to impose order through strict enforcement and (b) community policing and problem‐solving policing, where police attempt to produce order and reduce crime through cooperation with community members and by addressing specific recurring problems. This review examined the effects of disorder policing strategies compared to traditional law enforcement actions (e.g., regular levels of patrol) on the rates of crime, including property crime, violent crime, and disorder/drug crime. This review also examined whether policing disorder actions at specific locations result in crime displacement (i.e., crime moving around the corner) or diffusion of crime control benefits (i.e., crime reduction in surrounding areas).

neighborhoods and selected stretches of highways, and larger policedefined areas (e.g., precincts and divisions).

| What are the main findings of this review?
Do policing interventions focused on disorderly conditions reduce crime?
Yes, in addition to an overall reduction in crime, there is a reduction in property crime, violent crime, and disorder/drug crime when disorder policing interventions are implemented.
Do policing interventions focused on disorder result in crime being displaced or crime control benefits being diffused to surrounding areas?
Disorder policing interventions are associated with diffusion of crime control benefits in areas surrounding targeted locations. This conclusion is based on 15 tests that measured displacement or diffusion effects.
Of the two main strategies used in policing disorder, is one more effective than the other?
Yes, policing disorder through community and problem-solving is associated with reductions in crime. Aggressive, order maintenance approaches do not seem to generate crime reductions.

| What do the findings of this review mean?
The types of strategies used by police departments to address disorderly conditions seem to matter in controlling crime, and this holds important implications for police-community relations, justice, and crime prevention. Further research is needed to understand the key programmatic elements that maximize the capacity of these strategies to prevent crime.

| Objectives
To assess the effects of disorder policing interventions on crime.

| Search methods
Multiple search strategies were used to identify eligible studies.
These strategies included a keyword search of online abstract databases, hand searches of relevant journals, consultation with policing experts, and searches of bibliographies of past narrative, empirical, and systematic reviews of police crime prevention efforts.

| Selection criteria
Suitable interventions included tactics such as aggressive disorder enforcement as well as community and problem-oriented policing explicitly designed to control crime by addressing disorder. Studies that used randomized experimental or quasiexperimental designs were selected.

| Data collection and analysis
Twenty-eight studies containing 30 tests of disorder policing interventions were identified. A formal meta-analysis was conducted to determine the crime prevention effects of the eligible studies.

| Results
Policing disorder strategies are associated with an overall statistically significant, modest crime reduction effect. Community and problemsolving interventions generated crime reductions while aggressive order maintenance strategies did not.

| Authors' conclusions
The types of strategies used by police departments to address disorder seem to matter in controlling crime, and this holds important implications for police-community relations, justice, and crime prevention.

| Background
Crime policy scholars and practitioners have argued for years that when police address social and physical disorder in neighborhoods they can prevent serious crime, yet evaluations of the crime control effectiveness of disorder policing strategies yield conflicting results. This review reports on the results of the first systematic review and meta-analysis of the effects of disorder policing on crime.

| Objectives
To assess the effects of disorder policing interventions on crime. The review also examined whether policing disorder actions at specific locations result in crime displacement (i.e., crime moving around the corner) or diffusion of crime control benefits (i.e., crime reduction in surrounding areas).

| Search methods
A keyword search was performed on 15 online abstract databases.
Bibliographies of past narrative and empirical reviews of literature that examined the effectiveness of police crime control programs were reviewed and forward searches for works that cited seminal disorder policing studies were performed. Bibliographies of past completed Campbell systematic reviews of police crime prevention efforts and hand searches of leading journals in the field were performed. Experts in the field were consulted and relevant citations were obtained. This review includes eligible studies completed before 2013.

| Selection criteria
To be eligible for this review, interventions used to control disorder were limited to police enforcement efforts. Suitable police enforcement efforts included tactics such as directed patrol aggressive disorder enforcement as well as community and problem-oriented policing explicitly designed to control crime by addressing disorder. Studies that used randomized controlled experimental or quasiexperimental designs were selected. The control group in each study received routine levels of traditional police enforcement tactics.

| Data collection and analysis
Twenty-eight studies containing 30 tests of disorder policing interventions were identified and full narratives of these studies were reported. Nine of the selected studies used randomized experimental designs and 21 used quasiexperimental designs. A formal meta-analysis was conducted to determine the crime prevention effects of the eligible studies. Random effects models were used to calculate mean effect sizes.

| Results
Nineteen of 30 tests of disorder policing interventions reported noteworthy crime reductions. Our meta-analysis suggests that policing disorder strategies are associated with an overall statistically significant, modest crime reduction effect. The strongest program effect sizes were generated by community and problem-solving interventions designed to change social and physical disorder conditions at particular places. Conversely, aggressive order maintenance strategies that target disorderly behaviors by individuals in specific areas did not generate significant crime reductions. Crime displacement and diffusion effects were measured in 15 policing disorder tests. Our metaanalysis suggests disorder policing interventions are associated with diffusion of crime control benefits in areas surrounding targeted locations.

| Authors' conclusions
The types of strategies used by police departments to address disorder seem to matter in controlling crime, and this holds important implications for police-community relations, justice, and crime prevention. Further research is needed to understand the key programmatic elements that maximize the capacity of these strategies to prevent crime.

| The issue
Dealing with physical and social disorder, or "fixing broken windows," has become a central element of crime prevention strategies adopted by many American police departments (Kelling & Coles, 1996;Sousa & Kelling, 2006). The general idea of dealing with disorderly conditions to prevent crime is present in myriad police strategies.
These range from "order maintenance" and "zero-tolerance" policing, where the police attempt to impose order through strict enforcement, to "community" and "problem-oriented policing," where police attempt to produce order and reduce crime through cooperation with community members and by addressing specific recurring problems (Cordner, 1998;Eck & Maguire, 2006;Skogan, 2006). While its application can vary within and across police departments, disorder policing is now a common crime control strategy.
Most narrative reviews of the crime control effectiveness of policing disorder strategies suggest that the results are mixed (see, e.g., Harcourt & Ludwig, 2006;Kelling & Sousa, 2001). For instance, after reviewing a series of evaluations on the role disorder policing may have played in New York City's crime drop during the 1990s, the National Research Council's Committee to Review Police Policy and Practices concluded that these studies did not provide clear evidence of effectiveness (Skogan & Frydl, 2004). Given the mixed policy evaluation findings, and the popularity of policing disorder, a systematic review of the existing empirical evidence seems warranted. In this review, we synthesize the existing published and unpublished empirical evidence on the effects of disorder policing interventions and provide a systematic assessment of the crime reduction potential of these strategies.

| Policing disorder
New York City has been center stage in policy and scholarly debates about policing disorder and the broken windows perspective (most recently, see Rosenfeld, Terry, & Chauhan, 2014;Zimring, 2012).
While local officials and national observers attribute the city's violent crime drop in the 1990s to the adoption of a disorder policing strategy, many academics argue that it is difficult to credit this specific strategy with the surprising reduction in violent crime. The New York Police Department (NYPD) implemented the disorder policing strategy within a larger set of organizational changes framed by the Compstat management accountability structure for allocating police resources (Silverman, 1999). As such, it is difficult to disentangle the independent effects of disorder policing relative to other strategies implemented as part of the Compstat process  the crime drop (Bowling, 1999). Some academics have argued that the crime rate was already declining in the city before the implementation of police reforms, and that the city's decline in homicide rates was not significantly different from declines experienced in surrounding states and in other large cities that did not implement aggressive enforcement policies during that time period (Baumer & Wolff, 2014;Eck & Maguire, 2006 Harcourt and Ludwig (2006) and Greenberg (2014) report no statistically significant violence reduction impacts associated with the NYPD strategy. While this body of evidence seems to suggest that the NYPD policing disorder strategy may have generated violence reduction impacts, the magnitude of effects remains unclear.

| How the intervention might work
In their seminal "broken windows" article, Wilson and Kelling (1982) argue that social incivilities (e.g., loitering, public drinking, and prostitution) and physical incivilities (e.g., vacant lots, trash, and abandoned buildings) cause residents and workers in a neighborhood to be fearful. Fear causes many stable families to move out of the neighborhood and the remaining residents isolate themselves and avoid others. Anonymity increases and the level of informal social control decreases. The lack of control and escalating disorder attracts more potential offenders to the area and this increases serious criminal behavior. Wilson and Kelling (1982) argue that serious crime develops because the police and citizens do not work together to prevent urban decay and social disorder.
Several scholars suggest a strong need to establish a clearer distinction between crime and disorder (e.g., see Gau and Pratt, 2000). This comes up in the context of observational studies as well as evaluation studies. Here, the matter is about trying to avoid confounding measures of disorder with measures of crime. This remains a salient critique of the broken windows perspective. Weisburd et al. (2015), for instance, propose that the focus should be on serious crime and violent crime in particular; less serious crime should not be measured. They also call for a greater focus on physical disorder and more direct measures, including loitering, disorderly conduct, and drinking or intoxication.
The available research evidence on the theoretical connections between disorder and more serious crime is mixed. In the Netherlands, Keizer et al. (2008) conducted six field experiments examining the links between disorder and more serious crime and concluded that dealing with disorderly conditions was an important intervention to halt the spread of further crime and disorder. Skogan's (1990) survey research found disorder to be significantly correlated with perceived crime problems in a neighborhood even after controlling for the population's poverty, stability, and racial composition.
Further, Skogan's (1990) analysis of robbery victimization data from 30 neighborhoods found that economic and social factors' links to crime were indirect and mediated through disorder. In his reanalysis of the Skogan data, Harcourt (2001Harcourt ( , 2001) removed several neighborhoods with very strong disorder-crime connections from Newark, New Jersey, and reported no significant relationship between disorder and more serious crime in the remaining neighborhoods. Eck and Maguire (2006) suggest that Harcourt's analyses do not disprove Skogan's results; rather his analyses simply document that the data are sensitive to outliers. Indeed, the removal of different neighborhoods from Harcourt's analysis may have strengthened the disorder-crime connection (Eck & Maguire, 2006).
In his longitudinal analysis of Baltimore neighborhoods, Taylor (2001) finds some support that disorderly conditions lead to more serious crime. However, these results varied according to types of disorder and types of crime. Taylor (2001) suggests that other indicators, such as initial neighborhood status, are more consistent predictors of later serious crimes. Using systematic social observation data to capture social and physical incivilities on the streets of Chicago, Sampson and Raudenbush (1999) found that, with the exception of robbery, public disorder was not significantly related to most forms of serious crime when neighborhood characteristics such as poverty, stability, race, and collective efficacy were considered.
Sampson and Raudenbush's findings have been criticized because their social observation data on disorder were collected during the day rather than at night (Sousa & Kelling, 2006), as well as based on their decision to test a model in which disorder mediates the effects of neighborhood characteristics on crime rather than neighborhood characteristics mediating the effects of disorder on crime (Jang & Johnson, 2001). In another analysis, Xu et al. (2005) point out that Sampson and Raudenbush's (1999) results actually are supportive of broken windows theory.
Research on high activity crime places reveals that disorder clusters in space and time with more serious crimes. In their closer look at crime in Minneapolis hot spots, Weisburd et al. (1992) found that assault calls for service and robbery of person calls for service were significantly correlated with "drunken person" calls for service.
In Jersey City, New Jersey, Braga et al. (1999) found that highactivity violent crime places also suffered from serious disorder problems. The concentration of disorder in small places provides compelling opportunities for criminals. As Braga (2008) describes, abandoned buildings and vacant lots provide unguarded places for drug dealers selling their product and concealment for robbers looking to ambush an unsuspecting passerby. Disorder policing strategies that modify the crime opportunity structure at specific places by addressing social incivilities and physical incivilities could have important impacts on criminal behavior.

| Why it is important to do the review
The scientific research evidence on the crime control effectiveness of broad-based disorder policing strategies, such as quality-of-life programs and order maintenance enforcement practices, is mixed.
While nonexperimental evidence seems to suggest that the NYPD policing disorder strategy may have generated violence reduction impacts, the magnitude of effects remains unclear. More rigorous policy evaluations implemented in other jurisdictions support the perspective that dealing with disorderly conditions generates crime control gains. Two separate randomized controlled trials of disorder policing strategies implemented within a problem-oriented policing framework found the strategy resulted in significant reductions in calls for service to the police in Jersey City, New Jersey (Braga et al., 1999), and Lowell, Massachusetts (Braga & Bond, 2008).
A quasiexperimental evaluation of the Safer City Initiative, an intervention launched by the Los Angeles Police Department to reduce homeless-related crimes by addressing disorderly conditions associated with homeless encampments, generated modest reductions in violent, property, and nuisance street crimes (Berk & MacDonald, 2010). Other macro-level analyses have generated results supportive of broad-based policing disorder strategies. In California, controlling for demographic, economic, and deterrence variables, a county-level analysis revealed that increases in misdemeanor arrests was associated with significant decreases in felony property offenses (Worrall, 2002). Finally, an analysis of robbery rates in 156 American cities revealed that aggressive policing of disorderly conduct and driving under the influence reduces robbery (Sampson & Cohen, 1988).
Other evaluations have not found significant crime prevention gains associated with broad-based policing disorder strategies.
A recent reanalysis of the Kelling and Sousa (2001) data did not find that a generalized broken windows strategy, as measured by increased misdemeanor arrests, yielded significant reductions in serious crimes in New York City between 1989 and 1998 (Harcourt & Ludwig, 2006). An evaluation of a quality-of-life policing initiative focused on social and physical disorder in four target zones in Chandler, Arizona, did not find any significant reductions in serious crime associated with the strategy (Katz, Webb, & Schaefer, 2001).
An evaluation of a 1-month police enforcement effort to reduce alcohol and traffic-related offenses in a community in a Midwestern city did not find any significant reductions in robbery or burglary in the targeted area (Novak, Hartman, Holsinger, & Turner, 1999).
Similarly, a randomized controlled experiment of broken windows policing in three towns in California (Redlands, Colton, and Ontario) found no significant effects on fear of crime, police legitimacy, collective efficacy, or perceptions of crime and social disorder .
Disorder policing strategies are common crime prevention interventions implemented by police departments across the world.
Given the ubiquity of disorder policing and the mixed program evaluation findings presented here, a systematic review of the existing empirical evidence is warranted.   responses (e.g., random patrol, rapid response, and ad-hoc investigations) and opportunistic community problem-solving responses. While disorder interventions developed from community policing initiatives may be present in certain control areas, none of the control areas can engage disorder policing strategies as their main approach to address crime problems.

| Types of areas
Only area-level studies were included in our systematic review.
Eligible areas can range from small places (such as hot spots comprised of clusters of street segments or addresses) to police defined areas (such as districts, precincts, sectors, or beats) to larger In the Jersey City and Lowell randomized controlled trials, the units of analysis were crime "hot spots" comprising street block faces and street intersections (Braga et al., 1999;Braga & Bond, 2008).
It is important to note that this heterogeneity in the units of analysis across studies could have varying and policy-relevant effects on crime prevention outcomes associated with the policing disorder strategies. As such, we classified the types of areas to ensure that the review is measuring similar findings across the potentially diverse set of locations subjected to treatment. We distinguished between small areas such as hot spots and buildings, smaller police-defined units (such as beats), larger police-defined units (such as districts and precincts), larger areas (such as neighborhoods and communities), and other spatial units.

| Types of interventions
The general idea of dealing with disorderly conditions to prevent crime is present in myriad police strategies, ranging from "order maintenance" and "zero-tolerance," where the police attempt to impose order through strict enforcement, to "community" and "problem-oriented policing" strategies, where police attempt to produce order and reduce crime through cooperation with community members and by addressing specific recurring problems (Cordner, 1998;Eck & Maguire, 2006;Skogan, 2006;Skogan et al., 1999). Problem-oriented policing programs that did not attempt to control crime by reducing disorder were excluded from this review.
We considered all policing programs that attempt to reduce crime through addressing physical disorder (vacant lots, abandoned buildings, graffiti, etc.) and social disorder (public drinking, prostitution, loitering, etc.) in neighborhood areas. These interventions were compared to other police crime reduction efforts that do not attempt to reduce crime through reducing disorderly conditions, such as traditional policing (i.e., regular levels of patrol, ad-hoc investigations, etc.). Since area-level studies were included in this review, particular attention was paid to studies that measured spatial crime displacement effects and diffusion of crime control effects. Policing strategies focused on specific locations have been criticized as resulting in displacement (see Reppetto, 1976). Academics have observed that crime prevention programs may result in the complete opposite of displacement-that crime control benefits were greater than expected and "spill over" into places beyond the target areas (Clarke & Weisburd, 1994). The quality of the methodologies used to measure displacement and diffusion effects, as well as the types of displacement examined (spatial, temporal, target, modus operandi), were assessed.

| Search methods for identification of studies
To identify the studies meeting the criteria of this review, several search strategies were used. First, a keyword search was performed on an array of online abstract databases (see lists of keywords and databases below). Second, the bibliographies of past narrative and empirical reviews of literature that examined the effectiveness of police crime control programs were reviewed (e.g., Braga, 2008  and reviewing the studies as described later, the list of studies meeting our eligibility criteria was emailed (in July 2013) to leading criminology and criminal justice scholars knowledgeable in the area of disorder policing strategies. These 120 scholars were defined as those who authored at least one study that appeared on our inclusion list, anyone involved with the National Academy of Sciences review of police research (Skogan & Frydl, 2004), and other leading scholars (see Appendix 1). This helped to identify any studies overlooked by the above searches-as these experts may be able to make referrals to studies that were missed, particularly unpublished studies.
Finally, an information specialist was engaged at the outset of our review and at points along the way to ensure that appropriate search strategies were used to identify the studies meeting the criteria of this review. For instance, we worked with the information specialist to conduct an extensive Google search for eligible studies by using the search terms below, as well as including words such as "research," "evaluation," and

Academic Search Premier
The following terms were used to search the above databases:

| Determination of independent findings
One problem in conducting meta-analyses in crime and justice is that investigators often do not prioritize outcomes examined. This is common in studies in the social sciences in which authors consider it good practice to report all relevant outcomes. For example, the Jersey City DMAP experiment presents an array of outcome measures, including violence, property, disorder, and narcotics calls for service (Weisburd & Green, 1995). However, the lack of prioritization of outcomes in a study raises the question of how to derive an overall effect of treatment. Specifically, the reporting of one significant result may reflect a type of "creaming" in which the authors focus on one significant finding while ignoring the less positive results of other outcomes. But authors commonly view the presentation of multiple findings as a method for identifying the specific contexts in which the treatment is effective. When the number of such comparisons is small and therefore unlikely to affect the error rates for specific comparisons, such an approach is often valid.
All studies for which a standardized effect size could be obtained were analyzed using three approaches and served as a sensitivity analysis to evaluate the effects of input variation on the output variation. The first approach is conservative; we calculated an overall mean effect size for each study that analyzed. This approach is the most conservative and likely underestimates the effect of disorder policing programs on crime.
It was used here primarily to provide a lower bound to the review findings.

| Treatment of qualitative research
Qualitative research on crime and disorder outcomes was not included in this systematic review. The authors hope that a qualitative researcher will assist in future updates to this review with a synthesis of qualitative evaluation measures.         Table 4). Prior to a discussion of the research findings, it must be noted that it is quite difficult to detect displacement effects, because the potential manifestations of displacement are varied. As Barr and Pease (1990) suggest, "if, in truth, displacement is complete, some displaced crime will fall outside the areas and types of crime being studied or be so dispersed as to be masked by background variation… no research study, however

| Characteristics of selected studies
Property owners and building managers required to address illegal drug selling by dealing with physical and social disorder. 5.5-month intervention period. No threats to the integrity of the treatment period.
100 street blocks with a place on the block that was referred to the Beat Health Team as having a drug and/or blight problem.
Randomized controlled trial; control and treatment groups were each randomly allocated 50 street blocks within residential and commercial statistical blocks. Differences in differences analytic design; pre-post time periods were 21.5 months before and 12 months after 5.5 month intervention period. Multiple surveys were conducted on a various aspects of the police-community relation and individual fear of crime. Residents reported lower levels of perceived disorder and higher levels of satisfaction with the police.

Not measured
Unspecified Southeastern City Foot Patrol Project Esbensen (1987) Decreases in quality of life offenses but no statistically significant reduction in crime trend.
A survey was conducted to gauge levels of police professionalism, levels of support to the police, and police/ community relations. The author did not find changes in perceptions of the police based on the intervention.
Catchment areas for both the treatment and control areas were constructed -no specification on the size of the areas was provided. Difference in counts during the intervention period suggest a displacement effect.

| Study Implementation
Most of the eligible studies did not report any noteworthy implementation problems. Seven studies (25.0% of 28), however, did report potential      forest plot in Figure 4 shows that the overall effect size favors a diffusion of crime control benefits impact over a crime displacement effect impact;

| Risk of bias in included studies
the overall effect size is small but statistically significant (0.091, p < .05; 95% CI [0.072, 0.111). 5 The largest effect sizes suggesting diffusion of crime control benefits were generally estimated from hot spots policing program evaluations where policing disorder interventions were applied to very small high-activity crime places. A prior Campbell review found that hot spots policing programs were more likely to generate diffusion impacts rather than crime displacement impacts ).
Given the important distinction in methodological quality between the randomized controlled trials and quasiexperimental evaluation studies, we also examined research design as a moderator variable. Figure 5 presents a random effects model examining the two different types of evaluation designs included in this review. 6  However, the purported relationship between quasiexperimental designs and larger effect sizes has not been universally found (see, e.g., Shadish and Ragsdale, 1996).
F I G U R E 2 Random effects meta-analysis of the largest effects of policing disorder programs on crime 5 For the crime displacement and diffusion meta-analysis, Q = 2843.833, df = 14, p < .05, I 2 = 99.508; τ 2 < 0.001, SE = 0.001, τ = 0.022. 6 We used a random effects model for this comparison.  Moderator variables help to explain and understand differences across studies in the outcomes observed. Program type could be an influential moderator of the observed effect sizes in our meta-analysis.

| Publication bias
Publication bias presents a serious challenge to any review of evaluation studies (Rothstein, 2008). Our extensive search procedures, the use of an information retrieval specialist (Phyllis   should be symmetric about the grand mean effect size. If there is asymmetry, the trim-and-fill procedure imputes the missing studies, adds them to the analysis, and then recomputes the grand mean effect size. A visual inspection of the resulting funnel plot in Figure 7 indicates very minor asymmetry, with one study added to create symmetry. This altered marginally the overall mean effect size, These findings provide support for police paying attention to social and physical disorder when seeking to reduce more serious crimes in neighborhoods. Indeed, beyond disorder policing, these general ideas support key strategies and tactics employed by a wide range of recent police innovations, such as community policing, problem-oriented policing, third-party policing, and hot spots policing (see Weisburd & Braga, 2006). Police departments should continue to engage policing disorder strategies as part of their portfolio of strategies to reduce crime.

| Quality of the evidence
The overall quality of evidence presented in this review is robust.
Randomized controlled trial designs were used in almost one-third of eligible studies and among the quasiexperimental studies, many used rigorous evaluation methods. Positive crime control findings were observed for both experimental and quasiexperimental research designs.
Nearly two-thirds of eligible studies demonstrated that treatment and control units were similar at the baseline measurement period. There was no evidence that authors of eligible studies engaged in selective reporting of crime outcomes. Furthermore, evidence of contamination of treatment was absent in all of the eligible studies.

| Limitations and potential biases in the review process
Outcome measures by studies included in this review relied exclusively on official records and did not include measures of selfreport victimization. As such, our findings could be biased by police decision-making processes and other biases.

| Agreements and disagreements with other studies or reviews
The results of this systematic review support the general assertion that police can be effective in preventing crime (Skogan & Frydl, 2004) and the results are consistent with other Campbell Collaboration reviews on hot spots policing (Braga, 2007;), focused deterrence policing (Braga & Weisburd, 2012), problemoriented policing (Weisburd et al., 2008), and crime displacement (Bowers et al., 2011). Our conclusion that disorder policing is effective in controlling crime is consistent with some narrative reviews (e.g., Kelling & Coles, 1996), but diverges from other narrative reviews (Harcourt, 2001). In contrast to narrative reviews, systematic reviews and metaanalyses provide rigorous methodologies and statistical procedures to summarize, integrate, and interpret the overall findings of a welldefined set of scholarly works.
The findings of this review suggest that disorder policing strategies do generate crime control benefits. Perhaps of greatest interest to police leaders and policymakers alike is that the types of strategies used by police departments to control disorder seem to matter. Aggressive order maintenance strategies that target individual disorderly behaviors do not generate significant crime reductions. In contrast, community problem-solving approaches that seek to change social and physical disorder conditions at particular places produce significant crime reductions. These findings suggest that, when considering a policing disorder approach, police departments should adopt a "community co-production model" rather than drift toward a zero-tolerance policing model, which focuses on a subset of social incivilities, such as drunken people, rowdy teens, and street vagrants, and seeks to remove them from the street via arrest (Taylor, 2001). In devising and implementing appropriate strategies to deal with a full range of disorder problems, police must rely on citizens, city agencies, and others in numerous ways. As Taylor (2001) suggests, incivility reduction is rooted in a tradition of stable relationships with the community and responsiveness to local concerns. A sole commitment to increasing misdemeanor arrests stands a good chance to undermine relationships in low income, urban communities of color, where coproduction is most needed and BRAGA ET AL.

| Implications for research
The effect size difference noted by our analysis of the program type moderator variable should be regarded as a new hypothesis to be subjected to further testing rather than an established conclusion. Disorder problems, and the police programs designed to ameliorate disorderly conditions, are highly contextualized to local conditions. Moderator variables cannot be assumed to capture statistically independent conditions and, as such, great care must be taken when interpreting the relationship between moderator variables and effect sizes in meta-analysis (Lipsey, 2003). Our broad categorization of disorder policing programs into "community problem solving" and "aggressive order maintenance" interventions could be limited in two ways. First, the line between these two categories of disorder policing programs can be blurred. It is important to note that our systematic review was not designed to test the key theoretical propositions of the broken windows perspective on the links among disorder, fear, informal social control, and more serious crime in neighborhoods (Wilson & Kelling, 1982). Indeed, many of the effective policing disorder strategies reviewed here concentrate police action in crime hot spots. Deterrence and opportunity theories are usually applied to understand the crime control gains generated by hot spots policing (Braga & Weisburd, 2010;Nagin, 2013). From the standpoint of crime control and prevention, of course, the distinctions among deterrence, opportunity reduction, and broken windows are irrelevant-it only matters whether an intervention "works" by increasing public safety (for an argument to this effect, see Miles & Ludwig, 2007). From the standpoint of theory, on the other hand, these distinctions are of paramount importance and the time is ripe to develop a rigorous body of evaluation evidence to understand the mechanisms associated with successful disorder policing programs (see Weisburd et al., 2015).
It is also noteworthy that the results of this systematic review and meta-analysis lend some credibility to the NYPD's claim that disorder policing was influential in reducing crime in New York City over the course of the 1990s. But explaining the city's crime drop over the last two decades remains a puzzling challenge to social

SOURCES OF SUPPORT
The authors received no financial support for the research, authorship, and/or publication of this review.

DECLARATIONS OF INTEREST
Welsh and Schnell have no vested interest in the outcomes of this review, nor any incentive to represent findings in a biased manner.
With colleagues, Braga has conducted two randomized controlled trials that found disorder policing, implemented within a problemoriented policing framework, to be effective in reducing citizen calls for service to the police in crime hot spots. Although Braga does not have an ideological bias toward the effectiveness of place-focused interventions, it may be uncomfortable for him to report findings in this review that contradict the findings of his experiment.