Background: Two of the most central questions in radicalization research are, (1) why do some individuals radicalize when most of those from the same groups or exposed to similar conditions do not? and (2) why do radicalized individuals turn to radical violence while the majority remain inert? It has been suggested that the answer to both questions lie in the cumulative and interactive effects of a range of risk factors. While risk assessment and counter-radicalization take a risk-protective factor approach, there is widespread debate as to what these factors are and which are most important. Objectives: This review has two primary objectives. 1) To identify what the putative risk and protective factors for different radicalization outcomes are, without any predeterminations. 2) To synthesize the evidence and identify the relative magnitude of the effects of different factors. The review's secondary objectives are to:. 1) Identify consistencies in the estimates of factors across different radicalization outcomes. 2) Identify whether any significant heterogeneity exists within factors between (a) geographic regions, and (b) strains of radicalizing ideologies. Search Methods: Over 20 databases were searched for both published and gray literature. In order to provide a more comprehensive review, supplementary searches were conducted in two German and one Dutch database. Reference harvesting was conducted from previous reviews and contact was made with leading researchers to identify and acquire missing or unpublished studies. Selection Criteria: The review included observational studies assessing the outcomes of radical attitudes, intentions, and/or radical behaviors in OECD countries and which provided sufficient data to calculate effect sizes for individual-level risk and protective factors. Data Collection and Analysis: One-hundred and twenty-seven studies, containing 206 samples met the inclusion criteria and provided 1302 effect sizes pertaining to over 100 different factors. Random effects meta-analyses were carried out for each factor, and meta-regression and moderator analysis were used to explore differences across studies. Results: Studies were primarily cross-sectional, with samples representing 20 countries OECD countries. Most studies examined no specific radicalizing ideology, while others focussed on specific ideologies (e.g., Islamist, right-wing, and left-wing ideologies). The studies generally demonstrated low risk of bias and utilized validated or widely acceptable measures for both indicators and outcomes. With some exceptions, sociodemographic factors tend to have the smallest estimates, with larger estimates for experiential and attitudinal factors, followed by traditional criminogenic and psychological factors. Authors' Conclusions: While sociodemographic factors are the most commonly examined factors (selective availability), they also tend to have the smallest estimates. So too, attitudinal and even experiential factors, do not have effect sizes of the magnitude that could lead to significant reductions in risk through targeting by interventions. Conversely, traditional criminogenic factors, as well as psychological factors tend to display the largest estimates. These findings suggest the need to broaden the scope of factors considered in both risk assessment and intervention, and this review provides much needed evidence for guiding the selection of factors.
Bibliographical noteFunding Information:
This study was supported by the DHS Science and Technology Directorate and the Five Research and Development (5RD) Countering Violent Extremism Network.
This study also received support by the European Commission's Horizon 2020 programme, Grant no. 699824.
© 2021 The Authors. Campbell Systematic Reviews published by John Wiley & Sons Ltd on behalf of The Campbell Collaboration