Police programmes that seek to increase community connectedness for reducing violent extremism behaviour, attitudes and beliefs

Abstract

Background

Police can play a role in tackling violent extremism through disrupting terrorist plots and by working with communities to identify individuals at risk of radicalisation. Police programmes to tackle violent extremism can involve a range of approaches and partnerships. One approach includes efforts to improve community connectedness by working to address social isolation, belonging, economic opportunities and norms and values that may lead people to endorse or support violent extremist causes and groups. The assumption is that the risk of an individual being radicalised in the community can be reduced when police work in pothe international legal ordersitive ways with community members and groups to mobilise and support activities that help generate a sense of belonging and trust. Police programmes that build a sense of belonging and trust may help ensure individuals are not influenced by activities that violent extremists use to attract support for their cause.

Objectives

The review aimed to systematically examine whether or not police programmes that seek to promote community connectedness are effective in reducing violent extremist behaviours, attitudes and beliefs. The review also sought to identify whether effectiveness varied by the intervention type and location.

Search Methods

Using terrorism‐related terms, we searched the Global Policing Database to identify eligible published and unpublished evaluations between January 2002 and December 2018. We supplemented this with comprehensive searches of relevant terrorism and counter‐terrorism websites and research repositories, reference harvesting of eligible and topic‐relevant studies, forward citation searches of eligible studies, hand‐searches of leading journals and consultations with experts.

Selection Criteria

Eligible studies needed to include an initiative that involved the police, either through police initiation, development, leadership or where the police were receivers of the programme (such as a training programme) or where the police delivered or implemented the intervention. The initiative also needed to be some kind of a strategy, technique, approach, activity, campaign, training, programme, directive or funding/organisational change that involved police in some way to promote community connectedness. Community connectedness was defined as being community consultation, partnership or collaboration with citizens and/or organisational entities. Eligible outcomes included violent extremism, along with radicalisation and disengagement which are considered to be attitudinal and belief‐based components of violent extremism. These outcomes could be measured via self‐report instruments, interviews, observations and/or official data. To be included, studies could utilise individuals, micro‐ or macroplaces as the participants. Finally, studies needed to provide a quantitative impact evaluation that utilised a randomised or quasi‐experimental design with a comparison group that either did not receive the intervention, or that received “business‐as‐usual” policing, no intervention or an alternative intervention.

Data Collection and Analysis

The systematic search identified 2,273 records (after duplicate removal). After systematic screening across two stages (title/abstract and full‐text), just one study (reported in two documents) met the review eligibility criteria. Standardised mean differences (SMD) were used to estimate intervention effects for this single study and risk of bias was assessed using the Cochrane Risk of Bias in Non‐Randomised Studies‐Interventions tool (ROBINS‐I).

Results

The single eligible study (n = 191) was a quasi‐experimental evaluation of the Muslim‐led intervention—World Organisation for Resource Development Education (WORDE)—conducted in the United States in 2015. The intervention comprised three components: community education, enhancing agency networks and multicultural volunteerism activities. Self‐report data were collected from youth and adults who were civically engaged, sensitised to issues of violent extremism and who had existing cooperative relationships with law enforcement and social services. The comparison group comprised matched participants who had not engaged with the WORDE programme. The outcomes most closely aligned with conceptual definitions of deradicalization, specifically levels of acceptance and/or engagement with cultural and religious differences or pluralistic views and modification of group or personal identity. Based on single survey items, the SMD ranged from small to medium in favour of the treatment group aside from one item which favoured the comparison group (“I make friends with people from other races”, SMD = −0.51, 95% CI: −0.82, −0.19). However, of the nine SMDs calculated, six had confidence intervals including zero. These effects should be interpreted with caution due to the study's overall serious risk of bias. It is important to note that it is not explicitly clear whether the evaluation participants in the treatment group were all directly exposed to the two intervention components that involved police. Hence, these evaluation outcomes may not be direct measures of how effect police were at countering violent extremism by promoting community connectiveness.

Conclusions

The aim of this systematic review was to examine whether or not police programmes that seek to promote community connectedness are effective in reducing violent extremist behaviours, attitudes and beliefs. There is insufficient evidence available to ascertain whether such interventions achieve these outcomes. This finding is the result of the fact that interventions that have been evaluated tend to be characterised by evaluation designs that do not adopt experimental or quasi‐experimental approaches or use outcomes that are outside of scope for this review. While the volume of studies identified provide support for the assertion that police can play a role in tackling violent extremism by participating in, and implementing, programmes that promote community connectedness, it is unclear at this time if such approaches work in reducing violent extremism. Whilst we conclude that investment needs to be made in more robust methods of evaluation to test for programme effectiveness, we acknowledge that conducting evaluation and research in the area of counter‐terrorism/violent extremism is challenging.

1. PLAIN LANGUAGE SUMMARY

1.1. There is limited evidence of how police programmes to generate community connectedness affect violent extremist behaviours, attitudes and beliefs

Police programmes to generate community connectedness are assumed to help reduce risk factors that lead individuals to radicalise to violent extremism. There is no robust body of evaluation evidence to verify this claim. This lack of evidence is because programme funders have not sufficiently invested in impact evaluations of policing programmes that aim to counter violent extremism by promoting community connectedness.

1.2. What is this review about?

Community connectedness and efforts to engage communities may help to mitigate the risk of individuals radicalising to violent extremism. Police, under some circumstances, can play a key role in programmes aimed at tackling violent extremism. This includes working with communities and other agencies to tackle social isolation, economic opportunity and norms and beliefs that lead individuals and groups to radicalise and support extremist causes.

This review looked at whether or not strategies involving police in the initiation, development or implementation of programmes aimed at community connectedness had an impact on reducing violent extremist beliefs and behaviours.

What is the aim of this review?

This Campbell systematic review examines whether police programmes aiming to improve community connectedness have an effect on violent extremist behaviour, attitudes and beliefs. It summarises evidence from one study that met the inclusion criteria and references others that describe types of interventions, but that have not been rigorously evaluated.

1.3. What studies are included?

The review includes studies that evaluated programmes aimed at countering violent extremism by promoting community connectedness. The interventions included in the review needed to have a police focus, where the intervention involved police as the receivers of an intervention and/or partners in the development, initiation and implementation of a programme. The intervention could be focused on individuals, places (e.g., schools), neighbourhoods or larger geographical locations.

Although the systematic search captured 2,273 potential studies, only one study met the review inclusion criteria. This study was conducted in 2015 in the USA.

1.4. What are the findings of this review?

The one included study was a Muslim community‐led initiative involving police that aimed to counter violent extremism through a community‐based education and awareness programme. The programme aimed to improve referral networks for agencies/third parties to help assist individuals identified as at‐risk of radicalisation.

Evidence from this study showed mixed small‐to‐medium effects on self‐reported deradicalization measures in favour of the treatment group. Eight out of nine calculated effect sizes favoured the intervention, though six of these were statistically insignificant. One survey item favoured the comparison group: “I make friends with people from other races”. However, these results need to be interpreted with caution due to the study limitations.

Given the low number of studies identified, the authors have also provided a summary of a small sample of studies reporting on interventions that aligned with the review topic but did not meet the inclusion criteria due to weak evaluation designs. These studies illustrate a range of approaches being used by the police, such as recreation and sports activities, and community education and engagement around countering violent extremism and related topics.

1.5. What do the findings of this review mean?

There is currently insufficient evidence to establish whether police programmes aimed at countering violent extremism by promoting community connectedness are effective. Although the evidence identified by this review shows that such programmes are being implemented, they have not yet been rigorously evaluated. Future research should aim to rigorously evaluate such initiatives.

1.6. How up‐to‐date is this review?

The review authors searched for studies up to December 2018.

2. BACKGROUND

2.1. The problem, condition or issue

Community engagement and connectedness are identified as potential mitigating factors for those at risk of engaging in violent extremism (Cherney & Hartley, 2017). A focus on inclusion, social connectedness and positive cultural norms is essential for prevention efforts designed to build inclusive communities and weaken the influence of extremist messages and recruiters (Grossman, Peucker, Smith, & Dellal, 2016; Van Den Bos, 2018; Schanzer, Kurzman, Toliver, & Miller, 2016). Growing research suggests that cohesive communities are resilient against violent extremist influences; for example, it is argued that a greater sense of belonging and acceptance can reduce extremist behaviour, attitudes and beliefs (Cherney, Bell, Leslie, Cherney, & Mazerolle, 2018; Grossman et al., 2016; Van Den Bos, 2018).

As frontline practitioners, police are well placed to promote social inclusion and social connectedness, and thereby preventing violent extremism. In the general policing literature, when police engagement with the public is undertaken in an inclusive and fair manner, police can be instrumental in fostering a deep understanding of the local communities they police, creating opportunities for improving community relations (Gill, Weisburd, Telep, Vitter, & Bennett, 2014). Strong police‐community relations are likely an important foundation for police being in a position to identify individuals who might be at risk of radicalisation and violent extremism and then work with community leaders to counter the influence of a variety of different types of violent extremist groups including those from the far right, the far left, environmental extremism, political and religious extremism groups. Police can, therefore, be key agents in promoting community connectedness, working with community members to build trust, minimise social distancing—particularly amongst culturally diverse communities—and strengthen a sense of belonging by showing that they have the interests of the community at heart (Cherney & Hartley, 2017; Murray, Mueller‐Johnson, & Sherman, 2015).

Increasingly, police are working with a range of different agencies, together actively engaging the community to reduce social isolation, improve economic opportunity and aim to create social and cultural norms that prevent violent extremism (Schanzer et al., 2016). Yet it is unclear whether or not the range of police initiatives that foster community connectedness are able to reduce violent extremism. Thus, it is essential to understand the effectiveness of policing programmes aimed at promoting community connectedness and their impact on reducing violent extremism.

2.2. The intervention

This review aimed to include any policing intervention that aims to promote community connectedness, which was defined by the presence of two components. First, the intervention must have had a policing focus, defined as some kind of a strategy, technique, approach, activity, campaign, training, programme, directive or funding/organisational change that involves police in some way (other agencies or organisations can be involved; Higginson, Eggins, Mazerolle, & Stanko, 2015). Police involvement was broadly defined as follows.

• Police initiation, development or leadership of the intervention.

• Police are receivers of the intervention (such as being the receivers of training programmes or on the receiving end of initiatives aimed to engage police in the activities of another agency) or the intervention is related, focused or targeted to police practices.

• Delivery or implementation of the intervention by police.

Second, the policing intervention must have aimed to promote community connectedness. For the purposes of this review, we defined the promotion of community connectedness to mean an intention to increase prosocial linkages or prosocial ties between either community members themselves, community members and police, or community members and people in businesses, houses of worship, schools or any other community‐based organisation. Other terminology that may be used to represent connectedness in the literature includes (Thomas, 2019) the following.

• Promotion of common values, norms and/or reciprocity.

• Promotion of social networks, collective efficacy, social cohesion or social capital.

• Promotion of shared problem solving or citizen engagement.

We anticipated that policing interventions aiming to promote community connectedness would likely overlap with initiatives labelled community policing (see Gill et al., 2014) or other policing approaches that often aim to enhance community connectedness (e.g., neighbourhood policing or legitimacy approaches). However, we specifically defined a policing intervention that aims to promote community connectedness as being characterised by community consultation, partnership or collaboration with citizens and/or organisational entities. Specific strategies may have included the following:

• community meetings or forums;

• developing partnerships with specific organisations (Fox, 2012);

• police liaison programmes involving community members (Cherney et al., 2018);

• police work with community leaders to enhance personal skills (e.g., self‐identity, self‐awareness and resilience), employment skills (e.g., teamwork and self‐awareness), or leadership skills (Thomas, 2019);

• routine police work (such as beat policing, foot patrols, community intelligence initiatives) that explicitly seek to promote community connectedness;

• specific initiatives—such as neighbourhood policing teams—that seek to promote community connectedness; or

• police legitimacy enhancing programmes that seek to promote a sense of belonging and inclusion within local communities.

2.3. How the intervention might work

Police programmes that seek to reduce violent extremist behaviours and beliefs through improving community connectedness aim to generate an impact by promoting an increased sense of prosocial belonging and inclusion amongst at‐risk groups. This causal pathway is underpinned by key perspectives in the literature that argue how people are treated by institutional authorities, such as police, has an impact on their sense of identity and belonging by making them feel accepted by broader society (Mazerolle et al., 2014).

Social identity theory and the group value model (see Tyler & Lind, 1992) demonstrates that the ways that police engage with citizens will differentially affect the way that people perceive the police and thereby their willingness to comply with directives (see also Bradford, Murphy, & Jackson, 2014; Huo, Smith, Tyler, & Lind, 1996).

Some research shows that procedural fairness is more important for those on the margins (De Cremer & Sedikides, 2005; Murphy, 2013). Other research finds that the procedural justice, social identity and legitimacy pathway is found amongst both those with high and low group identifications (Bradford et al. 2014). Outcomes of police initiatives that build a sense of belonging and inclusion are, therefore, assumed to act as protective factors against radicalisation by ensuring individuals are not influenced by the messaging and grievance narratives that violent extremists use to attract support. We acknowledge, however, Nagin and Telep's (2017) review of the evidence challenging the causal relationship between perceptions of procedurally just treatment of citizens by agents of the criminal justice system and perceptions of police legitimacy. These authors conclude that perceptions of procedurally just treatment are associated with perceptions of police legitimacy and legal compliance (see also Donner, Maskaly, Fridell, & Jennings, 2015; Jackson, Hough, Bradford, & Kuha, 2015; Tyler 2004; Tyler, Goff, & MacCoun, 2015), yet that these associations are not necessarily reflective of causal connections.

As it relates specifically to tackling violent extremism, the quality of police engagement with different types of communities—such as the Muslim community—has been shown to influence the degree to which people are willing to partner with police to tackle terrorism (Cherney & Murphy, 2017). Police are seen as legitimate authorities and representatives of the state and when they work with community groups. This helps builds police legitimacy and has a spill over effect on people's sense of belonging and inclusion.

2.4. Why it is important to do the review

Community engagement approaches have become a key component of police counter‐terrorism efforts (Cherney & Hartley, 2017). These strategies have emphasised community engagement and outreach to identify potential violent extremism threats. This has involved police programmes that aim to promote collaborative problem solving between police and community members to tackle radicalisation, such as through identifying youth at risk of radicalising to violent extremism (Cherney, 2018). For example, following 9/11, police units in Australia, the United Kingdom, the United States, and Canada were established to undertake outreach with particular community groups (e.g., Muslim communities), with the aim of tackling violence extremism by enhancing relations and connectedness between police and these communities, and also between community members (Cherney, 2018; Ramirez, 2012). However, to date, there has been no systematic synthesis of the evaluation evidence for these policing approaches and their impact on violent extremism.1 Therefore, the current review is necessary to ascertain whether policing interventions that seek to promote community connectedness are effective for reducing violent extremism behaviour, attitudes and beliefs. In addition, the results from this review can be used to inform future decision making relating to both the design and evaluation of police programmes by identifying gaps in the evidence‐base and level of investment needed in evaluation of primary studies.

3. OBJECTIVES

The primary objective of this review was to answer the question: how effective are police programmes that seek to increase community connectedness for reducing violent extremism attitudes, beliefs and behaviours? A secondary objective was to also examine whether the effectiveness of these interventions vary by the following factors: geographical location, target population and type of policing strategy used to promote connectedness.

4. METHODS

4.1. Criteria for considering studies for this review

4.1.1. Types of studies

This review includes quantitative impact evaluations that utilise a randomised experimental (e.g., RCTs) or a quasi‐experimental design with a comparison group that does not receive the intervention. We will include studies where the comparison group receives “business‐as‐usual” policing, no intervention or an alternative intervention (treatment–treatment designs).

Although not as robust as RCTs, “strong” quasi‐experiments can be used to provide causal inference when there are elements of the design that aim to minimise threats to internal validity (see Farrington, 2003; Shadish, Cook, & Campbell, 2002). Minimising threats to internal validity can include: controlling case assignment to treatment and control groups (regression discontinuity), matching characteristics of the treatment and control groups (matched control), statistically accounting for differences between the treatment and control groups (designs using multiple regression analysis) or providing a difference‐in‐difference analysis (parallel cohorts with pre‐test and post‐test measures). Therefore, we included the following “strong” quasi‐experimental designs in this review:

• cross‐over designs;

• regression discontinuity designs;

• designs using multivariate controls (e.g., multiple regression);

• matched control group designs with or without preintervention baseline measures (propensity or statistically matched);

• unmatched control group designs without preintervention measures where the control group has face validity;

• unmatched control group designs with pre‐post intervention measures that allow for difference‐in‐difference analysis;

• short interrupted time‐series designs with control group2 (less than 25 pre‐ and 25 postintervention observations; Glass, 1997);

• long interrupted time‐series designs with or without a control group (≥25 pre‐ and postintervention observations; Glass, 1997).

Weaker quasi‐experimental designs can be used to demonstrate the magnitude of the relationship between an intervention and an outcome. However, we excluded the following weaker quasi‐experimental designs due to their limitations in establishing causality.

• Raw unadjusted correlational designs where the variation in the level of the intervention is compared to the variation in the level of the outcome.

• Single group designs with pre‐ and postintervention measures.

4.1.2. Types of participants

We included studies that considered the impact of community connectedness policing interventions on the following population subjects:

• 1.individuals of any age, gender or ethnicity;
• 2.microplaces (e.g., street corners, buildings, police beats, street segments);
• 3.macroplaces (e.g., neighbourhoods or larger geographies).

This review aimed to include programmes focused on individuals and groups identified as at‐risk violent extremism due to beliefs and or associations, as well as those who have acted on those beliefs. This was to ensure we captured police programmes tackling different levels of violent extremism. However, to be included in the review, participants did not need to be classified at‐risk or have displayed extremist behaviours. We placed no limits on the geographical region reported in the study. Specifically, we included studies conducted in high‐, low‐ and middle‐income countries in the review.

4.2. Types of interventions

This review aimed to include any policing intervention that aims to promote community connectedness. Specifically, to be included in the review, a study must have met the following two intervention criteria.

• 1.Report on a policing intervention, defined as some kind of a strategy, technique, approach, activity, campaign, training, programme, directive or funding/organisational change that involves police in some way (other agencies or organisations can be involved; Higginson et al., 2015). Police involvement is broadly defined as:

• police initiation, development or leadership;

• police are receivers of the intervention or the intervention is related, focused or targeted to police practices; or

• delivery or implementation of the intervention by police.

• 2.Report on a policing intervention that aims to promote community connectedness. For the purposes of this review, we define the promotion of community connectedness to mean an intention to increase linkages or ties between either the community members themselves, or community members and police. Other terminology that may be used to represent connectedness in the literature includes (Thomas, 2019):

• promotion of common values, norms and/or reciprocity;

• promotion of social networks, collective efficacy, social cohesion and/or social capital; or

• promotion of shared problem solving or citizen engagement.

We anticipated that policing interventions aiming to promote community connectedness will include, more generally, community consultation, partnership or collaboration with citizens and/or organisational entities. Specific strategies may include (but are not limited to) the following.

• Community meetings or forums.

• Developing partnerships with specific organisations (Fox, 2012).

• Police liaison programmes involving community members (Cherney et al., 2018).

• Police work with community leaders to enhance personal skills (e.g., self‐identity, self‐awareness and resilience), employment skills (e.g., teamwork and self‐awareness) or leadership skills (Thomas, 2019).

4.2.1. Types of outcome measures

Primary outcomes

Terrorism is one outcome of violent extremism, which constitutes both a cognitive and behavioural component. In the literature, a distinction is made between radicalisation as constituting beliefs, while violent extremism is the behavioural outcome of those beliefs.

Hence, this review aimed to include studies where the measured outcome was violent extremist attitudes, beliefs and behaviour. For the purposes of this review, violent extremism was defined as “advocating, engaging in, preparing, or otherwise supporting ideologically motivated or justified violence to further social, economic, and political objectives” (Barker, 2015; Horgan, 2009; Khalil and Zeuthen 2016; United States Agency for International Development, 2016).

It is important to note that violent extremism is defined and captured differently across countries (e.g., Barker, 2015; Government Offices of Sweden, 2011; Lowe, 2017; Norwegian Ministry of Justice and Public Security, 2014; Public Safety Canada, 2018). In order to capture research on violent extremism across global contexts, we used either the study authors' definitions of outcomes or, in the case of ambiguity, consulted definitions used in each country's associated terrorism legislation or policies to guide the inclusion of studies with potentially eligible outcomes.

The review also aimed to include studies where the outcome was disengagement and/or deradicalization, which are often encompassed within conceptualisations of violent extremism (Klausen, Campion, Needle, Nguyen, & Libretti, 2016). Disengagement generally captures the behavioural aspect of extremism and refers to reducing or ceasing physical involvement in violent or radical activities (Horgan, 2009). In contrast, deradicalization is defined as the psychological shift in attitudes or beliefs (Horgan & Braddock, 2010). This can encompass a variety of ideologies, including: Islamist (or jihadist), far‐right (right‐wing), far‐left (left‐wing) and single issue (anti‐abortion, animal liberationists; National Consortium of the Study of Terrorism and Responses to Terrorism [START], 2018).

We included outcome data that were measured through self‐report instruments, interviews, observations and/or official data (e.g., arrests or convictions). Some examples of how violent extremism attitudes, beliefs and behaviour can be measured include the following.

• Official data taken from the Profiles of Radicalized Individuals in the United States (PIRUS),3 which includes: active participation in operational plots intending to cause causalities (e.g., gathering weapons, choosing targets), recruiting individuals to an official or unofficial extremist group and providing material/financial support to extremist organisations (START, 2018).

• Level of disillusionment with, disappointment with, or renouncement of extremist group members, extremist leaders and/or radical ideology (Barrelle, 2015; Berger, 2016; San, 2018).

• Willingness to engage in violence (San, 2018).

• Modification of group and personal social identity (Barrelle, 2015).

• Level of acceptance and/or engagement with cultural and religious differences or pluralistic views (Barrelle, 2015).

• Number and/or strength of ties with extremist social networks, extremist recruiters (Perliger & Pedahzur, 2011).

• Amount of extremist activity (San, 2018).

Secondary outcomes

No secondary outcomes were included in this review.

4.2.2. Duration of follow‐up

Studies were included regardless of the length of follow‐up after the intervention. If the length of follow‐up varied across studies, we had planned to group and synthesise studies with similar follow‐up durations. For example, short (e.g., 0–3 months postintervention), medium (>3 months, <6 months) and long‐term follow‐up (>6 months post intervention). However, no studies with follow‐up data were located by the review.

4.2.3. Types of settings

We aimed to include studies reporting on an impact evaluation of an eligible intervention using eligible participants, outcome(s) and an eligible research design in any setting. Where there were multiple conceptually distinct settings, we planned to synthesise the studies within the settings separately. However, there werer no variations in study settings.

We included studies written in any language that were identified by the search. We used Google Translate for the title and abstract screening stage to identify whether a non‐English language study was potentially eligible for review. Due to resource limitations, potentially eligible studies that were published in a language other than English were not translated in full to enable screening them for final eligibility. However, we used Google Translate to translate as much of the document as possible to determine final eligibility. For transparency, we include the references to any language‐other‐than‐English study that could not be unequivocally excluded using this approach in the “References to studies awaiting classification”. We included studies published between 2002 and 2018 in the review.

4.3. Search methods for identification of studies

The full search record for this review is provided in Appendix A in the Supporting Information Material. Searches were conducted between November 2019 and March 2020 and captured research between January 2002 and December 2018. Due to search functionalities of some websites, there was no ability to restrict searches to this date range, and so research from all publications years was assessed for eligibility.

4.3.1. Electronic searches

The search for this review was led by the Global Policing Database (GPD) research team at the University of Queensland (Elizabeth Eggins, Lorelei Hine and Lorraine Mazerolle) and the Queensland University of Technology (Angela Higginson). The University of Queensland is home to the GPD (www.gpd.uq.edu.au), which served as the main search location for this review. The GPD is a web‐based and searchable database designed to capture all published and unpublished experimental and quasi‐experimental evaluations of policing interventions conducted since 1950. There are no restrictions on the type of policing technique, type of outcome measure or language of the research (Higginson et al., 2015). The GPD is compiled using systematic search and screening techniques, which are reported in Higginson et al. (2015) and summarised in Appendices B and C in the Supporting Information Material. Broadly, the GPD search protocol includes an extensive range of search locations to ensure that both published and unpublished research is captured across criminology and allied disciplines.

Because the GPD includes experimental and quasi‐experimental studies that evaluate interventions relating to police or policing, with no limits on outcome measures, we used a broad search to capture studies for the review. Specifically, we searched the title and abstracts of the corpus of GPD full‐text documents that have been classified as reporting on a quantitative impact evaluation of a policing intervention between 2002 and 2018 using the following search terms: *terror* OR extrem* OR *radical*.

4.3.2. Searching other resources

We also employed additional strategies to extend the GPD search. This included the following.

• Searching trial registries (those not indexed by WHO, but listed on the Office for Human Research Protections website https://www.hhs.gov/ohrp/international/clinical-trial-registries/index.html.

• Searching counter‐terrorism organisation websites (see Table 1).

• Conducting reference harvesting on existing reviews, eligible studies and studies deemed as closely eligible for the current review.

• Forward citation searching for all eligible documents.

• Liaising with the Five Country Research and Development Network (5RD), and the Department of Homeland Security Advisory Board network for the Campbell Collaboration grants, to enquire about eligible studies that may not be publicly available.

• Personally contacting prominent scholars in the field and authors of eligible studies to enquire about eligible studies not yet disseminated or published.

• Hand‐searching the following journals to identify eligible documents published in the 12 months prior to the systematic search date that may not have been indexed in academic databases.

  • a.Critical Studies on Terrorism
  • b.Dynamics of Asymmetric Conflict
  • c.Intelligence and Counter Terrorism
  • d.International Journal of Conflict and Violence
  • e.Journal for Deradicalization
  • f.Journal of Policing
  • g.Perspectives on Terrorism
  • h.Police Quarterly
  • i.Policing—An International Journal of Police Strategies and Management
  • j.Policing and Society
  • k.Sciences of Terrorism and Political Aggression
  • l.Studies in Conflict and Terrorism
  • m.Terrorism and Political Violence

Table 1.

Grey literature search locations

Organisation	Website
Global Terrorism Research Centre (Monash University)	http://artsonline.monash.edu.au/gtrec/publications/
Triangle Centre on Terrorism and Homeland Security	https://sites.duke.edu/tcths/#
Department of Homeland Security	https://www.dhs.gov/topics
Public Safety Canada	https://www.publicsafety.gc.ca/index-en.aspx
National Consortium for the Study of Terrorism and Responses to Terrorism (START)	https://www.start.umd.edu/
Terrorism Research Centre	http://www.terrorism.org/
Global Centre on Cooperative Security	https://www.globalcentre.org/publications/
Hedayah	http://www.hedayahcentre.org/publications
RAND Corporation	https://www.rand.org/topics/terrorism.html?content-type=research
Radicalisation Awareness Network (RAN)	https://ec.europa.eu/home-affairs/what-we-do/networks/radicalization_awareness_network_en
RadicalizationResearch	https://www.radicalizationresearch.org/
Royal United Services Institute (RUSI)	https://rusi.org/
Impact Europe	http://impacteurope.eu/
National Criminal Justice Reference Service	https://www.ncjrs.gov/App/AbstractDB/AbstractDBSearch.aspx

4.4. Data collection and analysis

4.4.1. Selection of studies

Title and abstract screening

After removal of duplicates and ineligible documents types (e.g., book reviews, blog posts), all records captured by the systematic search were imported into review management software, SysReview (Higginson & Neville, 2014). Two review authors (EE and LH) screened the titles and abstracts for all records identified by the search according to the following exclusion criteria.

• 1.Ineligible document type.
• 2.Record is not unique (i.e., duplicate).
• 3.Record is not about policing terrorism, radicalisation or extremism.

Prior to screening the entire corpus of search results, both screeners assessed the same small set of records and compared their judgements to verify consistent decision making. Although all efforts were made to remove ineligible document types and duplicates prior to screening, automated and manual cleaning can be less than perfect. As such, the first two exclusion criteria were used to remove ineligible document types and duplicates prior to screening each record on substantive content relevance.

Most records indexed in the GPD have a pre‐existing full‐text document. However, records from the additional searches that were deemed as potentially eligible at the title and abstract screening stage progressed to literature retrieval, where attempts were made to locate the full‐text document. Where full‐text documents could not be retrieved via existing university resources, they were ordered through the review authors' university libraries. All potentially eligible records then progressed to full‐text eligibility screening. If the full‐text document could not be located, the abstract was used to assess whether the study met full‐text eligibility criteria. Where a decision could not unequivocally made about eligibility based on the abstract, the record was categorised as a study awaiting classification (see “References to studies awaiting classification” section).

Full‐text eligibility screening

The same two review authors (EE and LH) also screened the full‐text for potentially records for final eligibility according to the following exclusion criteria.

• 1.Ineligible document type.
• 2.Document does not evaluate a policing intervention that aims to promote community connectedness.
• 3.The evaluation does not report violent extremism attitudes, beliefs or behaviour as an outcome.

All efforts were made to remove ineligible document types in earlier stages. However, sometimes these types of records can progress into later stages of screening (e.g., where duplicate records are not adjacent during screening or where screeners cannot unambiguously determine whether a record is ineligible based on the title and abstract). Therefore, the first two exclusion criteria were used to remove ineligible document types and duplicates.

4.4.2. Data extraction and management

Two review authors (EE and LH) independently coded and extracted data from eligible studies within SysReview, using the coding form provided in Appendix D in the Supporting Information Material. Disagreements or inconsistencies were resolved by discussion with a third review author (AH). Broadly, studies were coded according to the following domains.

• 1.General study characteristics (e.g., document type and study location).
• 2.Participants (e.g., sample characteristics by condition).
• 3.Intervention (e.g., intervention components, intensity andf setting).
• 4.Outcomes (e.g., conceptualisation, mode of measurement and time‐points).
• 5.Research methodology (e.g., design, unit and type of assignment).
• 6.Effect size data.
• 7.Risk of bias.

4.4.3. Assessment of risk of bias in included studies

Two review authors (EE and LH) assessed risk of bias using the Cochrane Risk of Bias in Non‐Randomised Studies‐Interventions tool (ROBINS‐I), which guides rating across seven domains to determine low, moderate, serious, or critical risk of bias, or no information to make a judgement (Sterne et al., 2016). The confounding domain assesses whether the study accounts for the baseline and/or time‐varying prognostic factors (e.g., socioeconomic status). The selection domain refers to biases internal to the study in terms of the exclusion of some participants, outcome events, for follow‐up of some participants that is related to both intervention and outcome. The classification of interventions domain refers to differential (i.e., related to the outcome) or nondifferential (i.e., unrelated to the outcome) misclassification of the intervention status of participants. The measurement of outcomes domain assesses whether bias was introduced from differential (i.e., related to intervention status) or nondifferential (i.e., unrelated to intervention status) errors in the measurement of outcome data (e.g., if outcome measures were assessed using different methods for different groups). The deviations from intended interventions refers to differences arising in intended and actual intervention practices that took place within the study. The missing data domain measures bias due to the level and nature of missing information (e.g., from attrition, or data missing from baseline or outcome measurements). Finally, the selection of reported results domain is concerned with reporting results in a way that depends on the findings (e.g., omitting findings based on statistical significance or direction of effect). The results of the risk of bias assessment are provided in a written summary and table. If future updates of the review identify additional eligible studies, the results of the risk of bias assessment will also be depicted in a risk of bias summary figure.

4.4.4. Measures of treatment effect

There was only one eligible study, in which all outcome data were collected from individual participants, using continuous measures. The specific data required to calculate effect sizes were not included in the eligible study reports, but was provided by the study authors. Means, standard deviations and sample size for each group was used to calculate standardised mean differences (SMD) in RevMan, along with 95% confidence intervals.

4.4.5. Unit of analysis issues

Unit of analysis issues can arise where (a) multiple documents report on a single empirical study; (b) multiple conceptually similar outcomes are reported in the one document; (c) data are reported for multiple time‐points; and/or (d) studies have clustering in their research design. Based on the research included in this review, none of these issues were relevant when quantifying and synthesising treatment effects. Although the single included study was reported in two documents, only one document reported quantitative data and sufficient detail to enable data extraction. For future updates of this review, our approach for handling these issues is specified in the review protocol (Mazerolle et al., 2020).

4.4.6. Dealing with missing data

Where data were missing in relation to coding categories, study authors were contacted by email to obtain the data. The results section also specifies which data were obtained from published reports of a study and which data were obtained directly from study authors (not available in the public domain).

4.4.7. Assessment of heterogeneity

Due to the limited research included in this review, we were unable to assess heterogeneity. However, for updates of this review, our approach for handling these issues is specified in the review protocol.

4.4.8. Assessment of reporting biases

Due to the limited research included in this review, we were unable to assess reporting/publication biases. However, for updates of this review, our approach for handling these issues is specified in the review protocol.

4.4.9. Data synthesis

Due to the limited research included in this review, we were unable to conduct meta‐analyses. Rather, estimates of treatment effects for eligible outcomes are presented as single SMDs, with their corresponding confidence intervals. For updates of this review, our approach for handling these issues is specified in the review protocol.

4.4.10. Subgroup analysis and investigation of heterogeneity

We had planned to use subgroup analyses to assess whether the impact of the intervention varied by the following factors: geographical location, target population and type of policing strategy used to promote connectedness. However, due to the limited research included in this review, we were unable to conduct subgroup analyses. For updates of this review, our approach for conducting subgroup analyses is specified in the review protocol.

4.4.11. Sensitivity analysis

We had planned to use sensitivity analyses to assess the impact of risk of bias on estimates of the treatment effect. However, due to the limited research included in this review, we were unable to conduct these analyses. For updates of this review, our approach for conducting sensitivity analyses is specified in the review protocol.

4.5. Deviations from the protocol

Our review made six minor deviations from the protocol. First, despite intending to translate potentially eligible documents written in languages other than English, resources did not permit this approach. However, for transparency, the “References to studies awaiting classification” section lists all studies written in another language that could not be unequivocally excluded on their titles and/or abstracts or by attempts to translate documents via Google Translate.

Our second deviation was changing the hand searches of journals to 12 months prior to the end search date within the GPD and grey literature sources (i.e., December 2018). The protocol stated that the hand search would encompass the most recent four issues of each of the listed journals; however, conducting the hand search in this way would have included a nonequivalent sample of research (i.e., 2019 data, which was not captured by the remainder of the systematic search).

Our third deviation was using the full‐text eligibility criteria to screen the titles and/or abstracts of records that were retained after title and abstract screening, but where a full‐text could not be sourced to determine final eligibility. Records were only excluded in this way if an unequivocal decision could be made, otherwise, they were retained and included in the “References to studies awaiting classification” section.

Our fourth deviation was not contacting study authors where there was either missing information or “unclear” ratings during the risk of bias assessment. We chose this approach as the additional information would not have changed the overall risk of bias result. However, for updates of the review, we will follow the original protocol.

The fifth deviation was slightly changing the wording of the title and abstract screening criteria. In the protocol, the third criterion was “Document is not about terrorism or extremism”. While this wording was appropriate for records extracted from the GPD search because all records were impact evaluations relating to police or policing, this approach was overly sensitive for results captured by the grey literature and hand searching. Therefore, we changed the third title and abstract screening criterion to “Document is not about policing terrorism, radicalisation or extremism”.

The final deviation to the protocol is adding additional search steps in light of the low number of eligible studies identified by the systematic search and screening process. Specifically, we harvested the reference lists of excluded studies that were deemed to almost meet inclusion criteria (e.g., eligible intervention, no evaluation or ineligible outcomes) or that contained substantive content that was closely aligned with the review topic.

5. RESULTS

5.1. Description of studies

5.1.1. Results of the search

The results of search and subsequent screening are summarised in Figure 1. The search within the overall GPD systematic search identified 11,680 prior to any systematic processing that underpins the GPD (see Appendices B and C in the Supporting Information Material). Of these 6,038 were screened as being potentially about police or policing on their titles and abstract. A total of 5,352 full‐text English documents were located, with 686 unable to be located or written in a language other than English. Of the located full‐texts, 244 were screened as reporting on a quantitative impact evaluation of an intervention relating to police or policing, and deemed eligible for the GPD. For completeness, the GPD search component of this review includes both these GPD‐eligible studies and the records that were screened as being about police or policing on their title and abstract, but where a full‐text could not be located or was written in a language other than English. The GPD search results were combined with the records identified by the grey literature search, hand searches, reference harvesting and forward citation searching (n = 1,916) to generate a corpus of 2,273 records (after preliminary duplicate removal).

Figure 1.

Preferred Reporting Items for Systematic Reviews and Meta‐Analyses flowchart

A total of 1,142 records were screened on their title and/or abstract as being potentially about policing terrorism, radicalisation or extremism. We obtained the full‐text of 737 of these records via institutional libraries or correspondence with document authors, of which 71 were written in a language other than English. The full‐text for the remaining 405 records could not be located via institutional libraries or through contact with document authors (including n = 50 written in a language other than English). Of these, almost half were conference presentations or magazine articles, with the rest of evenly distributed amongst the following categories of document types: journal articles, books or book chapters, reports or working papers (government and technical), and theses. We handled the processing of records with no full‐text in two stages. First, we screened their titles and abstracts using the more specific full‐text screening criteria, which resulted in the exclusion of 313 records. These are recorded separately to the studies excluded on their full‐text in the “References to excluded studies” reference list. Second, we attempted to contact the authors of the remaining 92 records where we could not unequivocally exclude the record by screening the title and abstract using the full‐text screening criteria. Seven authors responded without providing a full‐text document, but confirmed that their research did not meet the review inclusion criteria. For the remaining 85 records: (a) authors could not provide the full‐text or recall whether the document met inclusion criteria; (b) no response was received from document authors; or (c) contact details for document authors could not be found. These documents are reported in the “References to studies awaiting classification” list. Of the 1,057 studies screened on the full‐text screening criteria, only one study met the review eligibility criteria (reported in two documents).

5.1.2. Included studies

The sole eligible study by Williams, Horgan, and Evans (2016) was conducted in Montgomery County, Maryland, United States in 2015. The study evaluated the impact of the World Organisation for Resource Development Education (WORDE) programme on violent extremism attitudes, beliefs and behaviours. This programme was a nonprofit organisation funded by the National Institute of Justice and led by a group of Muslim scholars and community leaders. The group also worked with experts in the areas of policy analysis, theology, academia and development. The programme was multipronged with three “interlocking” components. First, the programme provided community education with a town hall meeting component that included dialogue opportunities for public officials and members of the public. The educational component covered topics such as family support, youth engagement and conflict resolution. Second, the programme sought to enhance the capacity of agencies to create a referral network to identify and help individuals who are at risk of becoming radicalised or are at risk of committing violent offences. Agencies involved in this component of the intervention included law enforcement, community organisations and social services (e.g., social workers, psychologists). Third, the programme provided community members the opportunity to participate in organised volunteerism and/or multicultural activities, such as art projects around social change and work to assist the homeless. This component of the intervention did not explicitly involve law enforcement.

Participants were eligible for inclusion within this study if they resided in Montgomery County, Maryland. The WORDE programme targeted youth and adults who were civically engaged, sensitised to issues of violent extremism and who had existing cooperative relationships with law enforcement and social services. The programme aimed to foster and maintain these networks for participants. Treatment participants (n = 133) were invited to participate in the study by WORDE programme staff and a pre‐screening questionnaire was used by researchers to generate a stratified random sample of participants. Comparison participants (n = 58) were recruited through (a) interfaith partners not involved in WORDE; (b) public school list‐serves; and (c) electronic bulletin boards (e.g., Craigslist, Google Groups). The comparison group were considered to be engaged with other volunteerism or multicultural events and activities, but not with the specific WORDE programming.

The authors report that the groups were matched using propensity score matching using demographic characteristics age, race, religion and educational level; however, it is unclear whether this was implemented as intended. The groups were predominantly male (treatment = 75.9%; comparison = 51.7%) and aged in their midtwenties (treatment M = 26.54 years, comparison M = 27.33), and Caucasian (treatment = 91.7%, comparison = 57.9%).

Williams et al. (2016) assessed the WORDE intervention on behavioural outcomes (e.g., increased coping skills), attitudes (e.g., towards different religions or ethnicities) and knowledge of out‐group cultures. Self‐report surveys captured these outcomes at one time point (after an unknown period of engagement with the programme4) using a 14‐item measure constructed by the authors, the Brief Volunteer Program Outcome Assessment. Items were measured on a seven‐point Likert scale (“completely disagree” to “completely agree”) with higher mean values equating to more agreement with the statement. The specific items were as follows.

“Thinking of when you volunteer, please rate your level of agreement with the following statements:

• I feel welcome*

• I feel a part of something bigger than myself*

• I feel a sense of teamwork*

• I make friendships that are active beyond the event*

• I make friends with people from other races*

• I feel useful

• I have responsibilities

• I have leadership responsibilities

• I feel a sense of purpose

• I feel free of peer pressure*

• I feel accepted*

• I wouldn't feel lonely

• I wouldn't feel afraid to talk to others*

• I learn about cultures other than my own*” (p. 157)

Of the above items, nine were deemed as eligible outcomes (marked with asterisk) and were considered to fall under the general banner of deradicalization. Specifically, these items align with Barrelle's (2015) conceptualisation that is defined as the level of acceptance and/or engagement with cultural and religious differences or pluralistic views and modification of group or personal identity. It is important to note that it is not explicitly clear whether the evaluation participants in the treatment group were all directly exposed to the two intervention components that involved police. Hence, these evaluation outcomes may not be direct measures of how effective police were at countering violent extremism by promoting community connectiveness.

5.1.3. Excluded studies

Due to the number of records screened for final eligibility (n = 1,057), we are unable to describe the full body of excluded studies (see “References to excluded studies” section). Rather, this section describes a small set of studies that almost met the review inclusion criteria or described interventions closely aligned with the review topic (n = 29). A total of 24 were documents that contained substantive content about community‐oriented policing approaches for countering terrorism, extremism or radicalisation but that did not report on an original impact evaluation (Barclay, 2011; Warnes, 2016; McGarrell, Freilich, & Chermak, 2007; Miller, Toliver, & Schanzer, 2016; Radicalisation Awareness Network, 2016a, 2016b; Pisoiu, 2018; Public Safety Canada, 2013, 2018; Helmus et al., 2017; Hofman & Sutherland, 2018; Lenos & Keltjens, 2016a, 2016b, Schanzer et al., 2016; Schwartz, 2015; U.S. Department of Homeland Security, 2011, 2015a, 2015b; Appelboom, 2015; Briggs, 2010; Silk, Spalek, & O'Rawe, 2013; Weine, Polutnik, & Younis, 2015; Cherney et al., 2018; DuBois & Alem, 2017).

Example intervention approaches included the following.

• Connect Training Programme: Police and community members participate together in training around understanding community policing from the other's perspective and building positive relationships (Irvine, 2013, reported in Silk et al., 2013).

• Framing activities around COMPLETE Public Safety (COMmunity Partnerships with Law Enforcement To Enhance Public Safety), rather than countering violent extremism (Schanzer et al., 2016).

• Living Safe Together: Provided government funding for multiple community activities, including camps for Muslim youth involving police, and community leaders whereby they received educational talks as well as opportunities to form relationships with both the police officers and their peers (Cherney et al., 2018).

• More than a Game: Community‐based resilience partnership between police and an Australian Rules football club, which targeted Muslim youth. Comprised sporting activities (e.g., football, cricket, surfing), police mentoring around social skills and leadership, and police workshops (on topics such as cyberbullying, counter‐terrorism, conflict resolution; DuBois & Alem, 2017).

• Edmonton Resiliency Project: Collaborative intervention delivered by City of Edmonton, Edmonton Police Service and the Organisation for the Prevention of Violence. Conducts education, engagement and offline and online interventions (Public Safety Canada, 2018).

• Multiple community policing activities in Amhara, Ethiopia, focus on trust‐building, including organising watch patrols, adjudicating minor disputes, literacy training, public health and family education (Schwartz, 2015).

• Hotlines or online reporting for community to notify police of concerns relating to possible terrorist activity (Briggs, 2010).

• Engaging the community in dialogue around countering violent extremism via social media (Schanzer et al., 2016).

In addition, two studies reported on impact evaluations of eligible interventions but used ineligible outcomes to assess the intervention's effectiveness. For example, Aksu (2014) evaluated the impact of nine community policing activities (e.g., family visits, sporting events, visits to police units) within a counter‐terrorism context in Turkey using an unmatched control group on citizen perceptions of police procedural justice and legitimacy (see also Cherney & Murphy, 2017).

A sample of three studies also examined eligible intervention approaches but did not evaluate these using eligible research designs (Boyd‐MacMillan, 2016; Weine, Eisenman, Kinsler, Glik, & Polutnik, 2017; Pickering, Wright‐Neville, McCullouch, & Lentini, 2007). For example, Boyd‐MacMillan (2016) evaluated Being Muslim Being Scottish, a multi‐session skills course with participants from both the community and practitioners (e.g., police, social workers) using a single group pre/post research design on participants’ integrative complexity regarding views towards their self‐reported own and opposed communities. Alternatively, (Weine et al. 2015; Weine, Younis, & Polutnik, 2017) conducted a process evaluation of countering violent extremism tailored community policing activities conducted by the Los Angeles Police Department, which included a biannual police‐Muslim community organisation forum.

5.2. Risk of bias in included studies

Table 2 summarises the degree of bias and specific reasons for this rating across the seven domains, based on the standardised questions provided by the ROBINS‐I tool. Specifically, the study was rated as having serious risk of bias for the confounding, selection, classification of interventions, and measurement of outcomes domains. A lack of information or ambiguity in the available reports for the study or data provided by study authors led to a rating of “no information” for the deviations from intended interventions and the missing data domains. Finally, the selection of reported results was rated as having a moderate risk of bias. Overall, these ratings suggest that the single included study included in the review has a relatively serious risk of bias.

Table 2.

Results for risk of bias assessment

Risk of bias domain	Rating	Rationale
Confounding	Serious	No baseline assessment of outcome measures or other potential confounders that might influence engagement with the treatment or comparison condition activities. In addition, it is unclear if authors verified if comparison participants had no interaction with the treatment (World Organisation for Resource Development Education [WORDE] programme), which raises the risk of time‐varying confounding because participants may have received both interventions. While the authors state that propensity score matching was used, their published report and data provided by the authors for the purposes of this review do not allow for independent assessment of the propensity score matching. Specifically, the variables the authors use to “match” participants vary within the report are not clear. For example, one section states participants were matched on demographics and another section states the participants were matched on nine measures including: trust in police, political extremism, racism, resiliency and coping, emotional stability, amped political extremism, historical loss, religiosity, and religious dogmatism. The time of measurement for these potential confounders is also not clear (e.g., whether at the beginning and end of the intervention).
Selection	Serious	Participants were invited to participate in the evaluation after they had already begun engagement with the WORDE programme (treatment) and the treatment group was based on a stratified random sample from those who expressed interest in the study. One of the variables influencing selection included the frequency of attendance. Although authors sampled across regular, infrequent and “one‐timer” attendees, it is unclear how attendance might impact estimates of treatment effect.
Classification of interventions	Serious	Intervention and comparison group not clearly defined. Specifically, it is unclear whether authors verified whether comparison group participants had any contact or engagement with the WORDE programme. The specific treatment received by comparison group participants is not clearly articulated aside from other multicultural events or volunteerism activities. It is also unclear whether the information used to define the groups was recorded at the start of the intervention or after the intervention and evaluation was underway.
Deviations from intended interventions	No information	The intended intervention and actual implementation of intervention were reported by study authors. The authors outlined the aims and activities of WORDE programme, but do not discuss implementation challenges or changes made to implementation. The reported variation in attendance for WORDE participants is suggestive of adherence issues, but this is not unexpected in community interventions and the content of the intervention (countering violent extremism).
Missing data	No information	The published report of the study does not provide participant demographics. Data supplied by study authors suggests there was no attrition, but this could be not be independently verified.
Measurement of outcomes	Serious	Outcome measurement appears to be equivalent across groups. However, study authors developed the outcome measures based on interviews with WORDE participants (treatment group) and it is not clear whether the same participants are used for the evaluation and design of the instrument. In addition, the way participants answered the survey questions may have been influenced by their knowledge of and self‐selection into the treatment and evaluation.
Selection of reported result	Moderate	No prospectively published protocol for the study exists. The published report for the study does not provide the results of the between group analyses, but rather reports data for the treatment group and a statement that there were no statistically significant differences between the treatment and comparison group. Given this statement about lack of differences, it is unlikely that the reported effects or data provided by study authors for this review are selected on the basis of the results from multiple outcome measurements within the one domain, multiple analyses of the intervention‐outcome relationship, or different subgroups. Data was provided by authors upon request.

5.3. Synthesis of results

Table 3 provides the standardised mean differences (SMDs) and their associated 95% Confidence Intervals for each eligible self‐report survey item from the Williams et al. (2016) study. All effect sizes were calculated with RevMan using data provided directly by the study authors, specifically: propensity‐matched means, standard deviations, and number of participants in each group. Overall, the effect sizes were small to medium in size and favoured the treatment group, except for one item which favoured the comparison group (survey item: “I make friends with people from other races”). However, all but three of the SMDs have confidence intervals that include zero, which indicates a lack of statistically significant differences between treatment and comparison group participants for most survey items.

Table 3.

Impact of World Organisation for Resource Development Education programme on self‐report deradicalization outcomes

Survey item	Standardised mean difference	95% Confidence interval
I feel welcome	0.47	0.15 to 0.78
I feel part of something bigger than myself	0.11	−0.20 to 0.42
I feel a sense of teamwork	0.24	−0.07 to 0.55
I make friendships that are active beyond the event	0.21	−0.10 to 0.52
I make friends with people from other races	−0.51	−0.82 to −0.19
I feel free of peer pressure	0.88	0.56 to 1.20
I feel accepted	0.44	0.13 to 0.75
I wouldn't feel afraid to talk to others	0.44	0.13 to 0.75
I learn about cultures other than my own	0.25	−0.06 to 0.56

6. DISCUSSION

6.1. Summary of main results

Police programmes to tackle violent extremism can involve a range of approaches and partnerships. One approach includes efforts to improve community connectedness by working to address social isolation, belonging, economic opportunities, and norms and values that may lead people to endorse or support violent extremist causes and groups. The assumption is that the risk of an individual being radicalised in the community can be reduced when police work with community members and groups to mobilise and support activities that help generate a sense of belonging and trust. Police programmes that build a sense of belonging and trust may help ensure individuals are not influenced by activities that violent extremists use to attract support for their cause.

Our review identified 24 studies that nearly met the inclusion criteria but were ultimately excluded because they did not use rigorous experimental or quasi‐experimental evaluation methods. These studies are summarised in this report and indicate a wide array of practices that are being adopted by police in their efforts to improve community connectedness as a way to tackle violent extremism.

Our review only identified one study that met our inclusion criteria. The included study was conducted in the United States by a Muslim‐led organisation in partnership with police and other agencies. The programme aimed to counter violent extremism through an education and awareness campaign and by improving networks for agencies/third parties to help assist individuals identified as at‐risk of radicalisation. The awareness raising activities aimed to increase knowledge and understanding about violent extremism risk factors that would help to facilitate problem solving between police and community groups to better to identify risks within the community. Increasing prosocial linkages or ties between agencies, community members and police was aimed at ensuring these stakeholders could better work together when identifying and coming into contact with radicalised individuals. The purpose was to help generate greater involvement in responses to terrorism across various stakeholders. The included study used a quasi‐experimental design to compare programme participants to non‐participants on a range of self‐report measures comprised of items representative of deradicalization. Of the nine effect sizes calculated, all favoured the treatment group except for one which favoured the comparison group (survey item: “I make friends with people from other races”). The effect sizes were small to medium in size and only three did not have confidence intervals that included zero. It is important to note that it is not explicitly clear whether the evaluation participants in the treatment group were all directly exposed to the two intervention components that involved police. Hence, these evaluation outcomes may not be direct measures of how effective police were at countering violent extremism by promoting community connectiveness. Overall, our review demonstrates that there is a global lack of rigorous evaluation evidence to conclusively determine whether or not police‐involved programmes to tackle violent extremism through promoting community connectedness are effective.

6.2. Overall completeness and applicability of evidence

Just one study was identified that met our inclusion criteria. This study was undertaken in State of Maryland in the United States, which significantly limits our capacity to draw any generalisable conclusions from the results nor conduct any analysis of publication bias. The fact that we only identified one study also prevented our capacity to answer our secondary research question which was to identify whether effectiveness varied by the intervention type and location. It was not possible to assess the differential impact of policing interventions that target either individuals or places (either micro or macro).

The outcome measures included in the one eligible study were limited to self‐report attitudinal measures, which also limits our capacity to examine the full breadth of outcomes, including: direct behavioural outcomes representative of violent extremism, different components theorised to fall within radicalisation and disengagement, and outcomes measures in different modalities such as official administrative data. In addition, self‐reporting measures may increase the potential for bias specifically in relation to radical attitudes, behaviours or beliefs. Due to the high‐risk nature of this behaviour participants are less likely to answer on a truthful basis, especially if they do espouse radical beliefs and attitudes that could escalate to violence. Finally, the single included study was a multicomponent intervention whereby not all intervention components explicitly had police involvement. Therefore, any effects of the intervention on the measured outcomes may not be directly attributable to police efforts to enhance community connectedness.

6.3. Quality of the evidence

The single included study in this review was rated as having serious risk of bias, using the ROBINS‐I tool. The overall quality of evidence on the effects of police programmes to tackle violent extremism through efforts to improve community connectedness is weak and highly limited. Existing studies do not adopt randomised or rigorous experimental methods. While tackling the problem of violent extremism through improving community connectedness is argued as having merit and value in the existing literature (Cherney & Hartley, 2017; Murray et al. 2015; Pickering, McCulloch, & Wright‐Neville, 2008; Ramiriz, Quinlan, Malloy, & Shutt, 2013), the current review did not locate sufficient evidence to substantiate that police efforts in this area have an impact. We note that more randomised and rigorous quasi‐experiments with matched control groups/areas would improve the quality of evidence on police programmes to counter violent extremism by improving community connectedness.

Methods for evaluating counter‐terrorism initiatives can be particularly challenging due to the hard‐to‐reach nature of the population. In addition to the lack of formal evaluations, programmes that target violent extremism attitudes, beliefs and behaviours often lack appropriate methods and practices to measure impact or effectiveness. Programmes that adopt clear inclusions criteria and collect baseline data (Holdaway & Simpson, 2018) could increase the likelihood of formal evaluations on the impact of police and community connectedness on violent extremism. The existing body of evidence is largely a function of the fact few programmes in this area have been subject to any type of formal evaluation.

6.4. Limitations and potential biases in the review process

In general, there are no specific limitations or biases in the systematic review process. The use of the GPD is a significant asset to the current review. The GPD is a web‐based and searchable database designed to capture all published and unpublished experimental and quasi‐experimental evaluations of policing interventions conducted since 1950. There are no restrictions on the type of policing technique, type of outcome measure or language of the research (Higginson et al., 2015). The GPD is compiled using systematic search and screening techniques, which are reported in Higginson et al. (2015) and summarised in Appendices B and C in the Supporting Information Material. Broadly, the GPD search protocol includes an extensive range of search locations to ensure that both published and unpublished research is captured across criminology and allied disciplines. The systematic search and screening underpinning the GPD thus provides a robust basis for expediting systematic reviews related to police and policing. This particular review was enhanced further by additional search steps to identify grey literature or studies that may not have been indexed in the GPD.

One limitation of the review is that the review includes research published by December 31, 2018. The evaluation of policing interventions aimed at enhancing community connectedness to counter violent extremism may be a rapidly moving area of research, which may mean this review omits eligible studies conducted in 2019. Therefore, it will be important that this review is updated within 2–3 years to capture any new research, which will also facilitate more concrete conclusions about the effectiveness of policing interventions aimed at enhancing community connectedness to counter violent extremism.

6.5. Agreements and disagreements with other studies or reviews

Due to the limited nature of evaluation and review literature on the effectiveness of policing approaches aimed at enhancing community connectedness to counter violent extremism, the findings of this review do not reaffirm or contradict any existing review. However, this review does provide a framework for assessing future research, which will be captured in updates of this review.

7. CONCLUSIONS

Currently there exists little evidence to evaluate whether police efforts to counter violent extremism through promoting community connectedness are effective. However, this conclusion needs to be considered in light of the fact that programmes to counter violent extremism are very challenging to implement and evaluate, and the outcomes reported in this review are the result of the low investment made in rigorous evaluations, a problem recognised in the field more generally (Hofman & Sutherland, 2018).

7.1. Implications for practice and policy

Despite the findings of this review, further research is needed to ascertain whether police efforts to enhance community connectedness can counter violent extremism attitudes and beliefs. With the lack of an existing evidence base, a key question to be raised is the role of the police in such community‐based efforts. For instance, existing scholarship draws attention to the downside of counter‐terrorism community engagement with the Muslim community, which has seen police prioritise intelligence gathering on terrorist threats over more collaborative efforts that aim to address issues of concern to Muslim community members (Cherney & Hartley, 2017). Moreover, since 9/11, the war on terror has sometimes led to a deterioration in relations between the police and the Muslim community due to perceptions of police unfairly targeting Muslims (Cherney & Murphy, 2017). This erodes trust towards and cooperation with the police. This does not mean police should play no role in strategies to enhance community connectedness to tackle violent extremism. Yet it does raise the issue as to what precisely should be the role of police in managing complex issues such as violent extremism within their own communities (see Meares & Tyler, 2020).

Police often come into contact with individuals only after they have engaged in radical actions or behaviours. This suggests that police could be well placed to cultivate communities of “intimates” around those that are exhibiting radical characteristics (see Grossman, Stephenson, Street, & Zhang, 2015). Family members, close friends and community insiders are best placed to detect signs of change in thinking and behaviour and as Grossman and her colleagues (Grossman et al., 2016; Thomas, Grossman, Miah, & Christmann, 2017) suggest, there is much to be gained by police doing much more than they presently do to encourage community reporting of violent extremism. Hence, police involvement in efforts to build trust and connectedness within communities through organisations such as places of worship and educational institutions, can inspire trust and promote the willingness of friends, family members or known members of the community to work with police.

This highlights the importance of promoting community‐based approaches. However, currently we have limited evidence to help guide policy and practice around what types of interventions work to reduce violent extremist behaviours, attitudes and beliefs. Whilst we know that community policing strategies have positive effects on citizen satisfaction, perceptions of disorder, and police legitimacy (see Gill et al., 2014) our review demonstrates the need for more investment in the careful design and evaluation of the types of policing initiatives that might help promote social connectedness to reduce violent extremism behaviour, attitudes, and beliefs. This type of investment is needed to better inform policymakers and practitioners on how to both generate evidence‐based knowledge and inform the translation and implementation of best‐practises in countering violent extremism.

7.2. Implications for research

Conducting evaluation research in the area of countering violent extremism is particularly difficult (Koehler, 2017; Romaniuk & Chowdhury Fink, 2012). This review clearly demonstrates that far more rigorous evaluation research is required to ascertain whether policing programmes aiming to promote community connectedness are an effective approach for countering violent extremism behaviours, attitudes, and beliefs.

CONFLICT OF INTERESTS

Three of the review authors have internal roles within the Campbell Collaboration Crime and Justice Group. Lorraine Mazerolle is the Co‐Chair of the Crime and Justice Coordinating Group (CJCG), Angela Higginson is the Editor of the CJCG and Elizabeth Eggins is the Managing and Associate Editor of the CJCG. Consequently, Lorraine Mazerolle, Angela Higginson and Elizabeth Eggins were not involved in any editorial or internal Campbell Collaboration communications about this review. In addition, Adrian Cherney has published research that is closely linked with the review topic. To minimise potential bias, Adrian Cherney was not involved in the screening or coding of any studies for this review. The other authors declare that there are no conflict of interests.

AUTHOR CONTRIBUTIONS

All the authors developed the content. E. E., A. H., and L. H. contributed to systematic review methods. E. E. and A. H. contributed to statistical analysis. E. E., A. H., and L. H. contribted to information retrieval. Lorraine Mazerolle is a Professor of Criminology in the School of Social Science at the University of Queensland and current Co‐Chair of the Campbell Collaboration Crime and Justice Coordinating Group. She has won numerous US and Australian competitive research grants, including systematic reviews, on topics such as third‐party policing, police engagement with high‐risk people and disadvantaged communities, community regulation, problem‐oriented policing, police technologies, civil remedies, street‐level drug enforcement and policing public housing sites. Elizabeth Eggins is the Managing and Associate Editor of the Campbell Collaboration Crime and Justice Coordinating Group. Her research focuses on intervention evaluation through randomised experiments and systematic reviews, with a broad focus on crime and justice and social welfare. She has coauthored and managed numerous systematic reviews and she has particular expertise in systematic review methodology, analysis and information retrieval. Adrian Cherney is a Professor in the School of Social Science at the University of Queensland and an Australian Research Council (ARC) Future Fellow. His current research focuses on the evaluation of programmes aimed at countering violent extremism and he has undertaken research on the supervision of terrorist offenders in Australian who have been released into the community on parole. His ARC Future Fellowship aims to develop and test metrics and methods to evaluate case‐managed interventions targeting individuals who have been charged for a terrorist offence or have been identified as at risk of radicalising to violent extremism. He has secured both international and national competitive grants. Lorelei Hine is a Senior Research Assistant in the School of Social Science at the University of Queensland. She has assisted with the project management of several systematic reviews and comanages the Global Policing Database. This has provided her with expertise in both systematic review methodology and substantive content in relation to criminal justice interventions. Angela Higginson is a Senior Lecturer in the School of Justice, Faculty of Law, QUT and current editor of the Campbell Collaboration Crime and Justice Coordinating Group. She is an ARC Discovery Early Career Research Award (DECRA) fellow for 2018–2020, and her DECRA project examines the correlates and consequences of ethnically‐motivated youth hate crime in Australia. Much of her work has focused on policing and community processes for crime control, with a particular expertise in evaluation through systematic reviews and meta‐analysis. Emma Belton is a PhD student and Research Assistant in the School of Social Science at the University of Queensland. She has coauthored and worked on projects in the area of countering violent extremism (CVE), including the collection and analysis of data and evaluations of programmes aimed CVE.

Supporting information

Supporting information

Mazerolle L, Eggins E, Cherney A, Hine L, Higginson A, Belton E. Police programmes that seek to increase community connectedness for reducing violent extremism behaviour, attitudes and beliefs. Campbell Systematic Reviews. 2020;16:e1111. 10.1002/cl2.1111