1 École de criminologie Université de Montréal Montreal Quebec Canada.
2 Department of Psychology Université du Québec à Montréal Montreal Quebec Canada.
3 Department of Psychoeducation and Social Work Université du Québec à Trois-Rivières Trois-Rivières Quebec Canada.
4 Department of Psychology Philipps-Universität Marburg Marburg Germany.
5 Center for the Study of Learning and Performance Concordia University Montreal Quebec Canada.
6 Zentrum Technik Und Gesellschaft Technische Universität Berlin Berlin Germany.

Assessment of the risk of engaging in a violent radicalization/extremism trajectory has evolved quickly in the last 10 years. Guided by what has been achieved in psychology and criminology, scholars from the field of preventing violent extremism (PVE) have tried to import key lessons from violence risk assessment and management, while bearing in mind the idiosyncrasies of their particular field. However, risk tools that have been developed in the PVE space are relatively recent, and questions remain as to their level of psychometric validation. Namely, do these tools consistently and accurately assess risk of violent extremist acting out? To answer this question, we systematically reviewed evidence on the reliability and validity of violent extremism risk tools. The main objective of this review was to gather, critically appraise, and synthesize evidence regarding the appropriateness and utility of such tools, as validated with specific populations and contexts. Searches covered studies published up to December 31, 2021. They were performed in English and German across 17 databases, 45 repositories, Google, other literature reviews on violent extremism risk assessment, and references of included studies. Studies in all languages were eligible for inclusion in the review. We included studies with primary data resulting from the quantitative examination of the reliability and validity of tools used to assess the risk of violent extremism. Only tools usable by practitioners and intended to assess an individual's risk were eligible. We did not impose any restrictions on study design, type, method, or population. We followed standard methodological procedures outlined by the Campbell Collaboration for data extraction and analysis. Risk of bias was assessed using a modified version of the COSMIN checklist, and data were synthesized through meta-analysis when possible. Otherwise, narrative synthesis was used to aggregate the results. Among the 10,859 records found, 19 manuscripts comprising 20 eligible studies were included in the review. These studies focused on the Terrorist Radicalization Assessment Protocol (TRAP-18), the Extremism Risk Guidance Factors (ERG22+), the Multi-Level Guidelines (MLG-V2), the Identifying Vulnerable People guidance (IVP guidance), and the Violent Extremism Risk Assessment (VERA)-all structured professional judgment tools-as well as Der Screener-Islamismus, an actuarial scale. Studies mostly involved adult male participants susceptible to violent extremism (N = 1106; M = 58.21; SD = 55.14). The types of extremist ideologies endorsed by participants varied, and the same was true for ethnicity and country/continent of provenance. Encouraging results were found concerning the inter-rater agreement of scales in research contexts (kappas between 0.76 and 0.93), but one of the two studies that examined it in a field setting obtained disappointing results (kappas ranging between of 0.47 and 0.80). Content validity studies indicated that PVE risk tools adequately cover the risk factors and offending processes of individuals who go on to commit extremist violence. Construct validity analyses were few and far between, with results indicating that empirical divisions of scales did not match their conceptual divisions. The internal consistency of subscales was lackluster (Cronbach's alphas between 0.19 and 0.85), whereas full scales demonstrated acceptable internal consistency when assessed (0.80 for the ERG22+ and 0.64 for the IVP guidance). Only one study examined convergent validity, and it revealed a lack of convergence, primarily due to particularities of the scale under study (the MLG-V2). Discriminant validity analyses were exploratory in nature, but suggested that PVE risk tools might not be ideology-specific and may apply to both group and lone actors. Finally, although the TRAP-18 showed a relatively strong postdictive effect size (pooled r = 0.62 [0.35-0.77], p = 0.000), the results were highly heterogeneou