Background: Multiagency responses to reduce radicalisation often involve collaborations between police, government, nongovernment, business and/or community organisations. The complexities of radicalisation suggest it is impossible for any single agency to address the problem alone. Police-involved multiagency partnerships may disrupt pathways from radicalisation to violence by addressing multiple risk factors in a coordinated manner.
Objectives:1. Synthesise evidence on the effectiveness of police-involved multiagency interventions on radicalisation or multiagency collaboration 2. Qualitatively synthesise information about how the intervention works (mechanisms), intervention context (moderators), implementation factors and economic considerations. Search Methods: Terrorism-related terms were used to search the Global Policing Database, terrorism/counterterrorism websites and repositories, and relevant journals for published and unpublished evaluations conducted 2002-2018. The search was conducted November 2019. Expert consultation, reference harvesting and forward citation searching was conducted November 2020. Selection Criteria: Eligible studies needed to report an intervention where police partnered with at least one other agency and explicitly aimed to address terrorism, violent extremism or radicalisation. Objective 1 eligible outcomes included violent extremism, radicalisation and/or terrorism, and multiagency collaboration. Only impact evaluations using experimental or robust quasi-experimental designs were eligible. Objective 2 placed no limits on outcomes. Studies needed to report an empirical assessment of an eligible intervention and provide data on mechanisms, moderators, implementation or economic considerations. Data Collection and Analysis: The search identified 7384 records. Systematic screening identified 181 studies, of which five were eligible for Objective 1 and 26 for Objective 2.Effectiveness studies could not be meta-analysed, so were summarised and effect size