Reviewing Radicalization Research Using a Network Approach


  • Veronika Batzdorfer ZPID - Leibniz Institute for Psychology Information, Trier
  • Holger Steinmetz ZPID - Leibniz Institute for Psychology Information, Trier


Systematic Literature Review, Radicalization, Hypotheses, Network Analysis, Causal Inference


In an effort to discern determinants of political radicalization, scholars have discussed and investigated a considerable number of personal or contextual constructs. Yet the existing literature reviews on this topic have mainly focused on specific data sources and research approaches (e.g., survey research), whereas an integrative overview is still missing. This study provides a systematic review of 57 published studies while particularly focusing on differences in the prevalence of considered determinants across research approaches (i.e., survey approaches, experimental approaches, and digital trace data approaches). As an innovative approach to systematic review, we apply a network approach for analyzing the most prevalent constructs and related hypotheses in the literature. Network analysis is particularly useful in this context because, it allows the visualization of the structure of constructs and hypotheses proposed in the field as well as the identification of crucial concepts. The review reveals differences across empirical approaches and closes with a discussion of over- and underresearched constructs, their generalizability across research approaches, and potentials for future research. We conclude by recommending a stronger integration of constructs and perspectives as well as a more rigid consideration of causal inference.


Editorial Note: This article underwent a post-publication review and revision in response to criticism about problematic use of a closely related and previously published article. The corrected version was uploaded August 4, 2020.


Authors' Correction Note:

Reviewing Radicalization Research Using a Network Approach

Veronika Batzdorfer & Holger Steinmetz


In the corrected article, the authors respond to criticism regarding similarities in the literature search process and insufficient connections between a recent meta-analysis (Wolfowicz, Litmanovitz, Weisburd, & Hasisi, 2019) and the present paper. Although the present paper cited Wolfowicz et al. (2019) several times, these linkages were not presented well enough. In the corrected paper, these connections are emphasized in the following way:

1) In the introduction, we note that the review builds on the meta-analysis by Wolfowicz et al. (2019) and stress the add-on value of our paper and the possibilities of fruitfully integrating both studies

2) In the method section, we note the similarities of both reviews in the search process, data bases, and search terms

3) In the discussion section, we added a discussion in which we integrate results of both

Due to the correction, readers are now better informed about similarities and differences of our studies.

Wolfowicz, M., Litmanovitz, Y., Weisburd, D., & Hasisi, B. (2019). A field-wide systematic review and meta-analysis of putative risk and protective factors for radicalization outcomes. Journal of Quantitative Criminology, 1-41.


Ajzen, I. (2005). Attitudes, personality and behavior. Milton-Keynes, England: Open University Press.

Alfano, M., Carter, J. A., & Cheong, M. (2018). Technological seduction and self-radicalization. Journal of the American Philosophical Association, 4(3), 298-322.

Alizadeh, M., Weber, I., Cioffi-Revilla, C., Fortunato, S., & Macy, M. (2017). Psychological and personality profiles of political extremists. CoRR, abs/1704.00119.

Antonakis, J., Bendahan, S., Jacquart, P., & Lalive, R. (2010). On making causal claims: A review and recommendations. The Leadership Quarterly, 21, 1086-1120. doi:10.1016/j.leaqua.2010.10.010

Baier, D., Manzoni, P., & Bergmann, M. C. (2016). Einflussfaktoren des politischen Extremismus im Jugendalter. Rechtsextremismus, Linksextremismus und islamischer Extremismus im Vergleich. Monatsschrift für Kriminologie und Strafrechtsreform, 99(5), 171-198.

Batzdorfer, V., Steinmetz, H., & Bosnjak, M. (2020). Big Data in der Radikalisierungsforschung: Eine systematische Übersichtsarbeit. [Big Data in radicalization research: A systematic review]. Psychologische Rundschau, 71(2), 96-102.

Bavelas, A. (1950). Communication patterns in task‐oriented groups. The Journal of the Acoustical Society of America, 22(6), 725-730.

Beller, J., & Kröger, C. (2018). Religiosity, religious fundamentalism, and perceived threat as predictors of Muslim support for extremist violence. Psychology of Religion and Spirituality, 10(4), 345.

Bhui, K., Otis, M., Silva, M. J., Halvorsrud, K., Freestone, M., & Jones, E. (2019). Extremism and common mental illness: Cross-sectional community survey of White British and Pakistani men and women living in England. The British Journal of Psychiatry, 1-8.

Borgatti, S. P., Mehra, A., Brass, D. J., & Labianca, G. (2009). Network analysis in the social sciences. Science, 323(5916), 892-895. doi:10.1126/science.1165821.

Borsboom, D., & Cramer, A. O. J. (2013). Network analysis: An integrative approach to the structure of psychopathology. Annual Review of Clinical Psychology, 9(1), 91-121. doi:10.1146/annurev-clinpsy-050212-185608.

Borum, R. (2011). Radicalization into violent extremism I: A review of social science theories. Journal of strategic security, 4(4), 7-36.

Burt, R. (2000). The network structure of social capital. Research in Organizational Behavior, 22, 345-423.

Cattell, R. B. (1978). The Scientific Use of Factor Analysis in Behavioral and Life Sciences, Plenum, New York.

Christmann, K. (2012). Preventing religious radicalisation and violent extremism: A systematic review of the research evidence. Research Report. Youth Justice Board.

Cheung, M. W. L., & Chan, W. (2005). Meta-analytic structural equation modeling: A two-stage approach. Psychological Methods, 10(1), 40-64.

Constantini, G., Richetin, J., Borsboom, D., Fried, E. I., Rhemtulla, M., & Perugini, M. (2015). Development of indirect measures of conscientiousness: Combining a facets approach and network analysis. European Journal of Personality, 29(5), 548-567.

Coid, J. W., Bhui, K., MacManus, D., Kallis, C., Bebbington, P., & Ullrich, S. (2016). Extremism, religion and psychiatric morbidity in a population-based sample of young men. The British Journal of Psychiatry, 209(6), 491-497.

Cooper, H. (2017). Research synthesis and meta-analysis: A step-by-step approach (Fifth ed.). Los Angeles, CA, USA: Sage.

Corner, E., & Gill, P. (2015). A false dichotomy? Mental illness and lone-actor terrorism. Law and Human Behavior, 39(1), 23-34.

Dechesne, M. (2009). Explorations in the experimental social psychology of terrorism: The struggle-violence link and its predictors. Revue Internationale de Psychologie Sociale, 22(3-4), 87-102.

Desmarais, S. L., Simons-Rudolph, J., Brugh, C. S., Schilling, E., & Hoggan, C. (2017). The state of scientific knowledge regarding factors associated with terrorism. Journal of Threat Assessment and Management, 4(4), 180.

Doosje, B., Loseman, A., & Van den Bos, K. (2013). Determinants of radicalization of Islamic youth in the Netherlands: Personal uncertainty, perceived injustice, and perceived group threat. Journal of Social Issues, 69(3), 586-604.

Egan, V., Cole, J., Cole, B., Alison, L., Alison, E., Waring, S., & Elntib, S. (2016). Can you identify violent extremists using a screening checklist and open-source intelligence alone? Journal of Threat Assessment and Management, 3(1), 21-36.

Ellis, B. H., Bixby, C., Miller, A., & Sideridis, G. (2016). Understanding pathways to and away from violent radicalization among resettled Somali refugees. Boston: Boston Children's Hospital.

Elwert, F. (2013). Graphical causal models. In S. L. Morgan (Ed.), Handbook of causal analysis for social research. (pp. 245-273). Dordrecht Heidelberg New York London: Springer.

Elwert, F., & Winship, C. (2014). Endogenous selection bias: The problem of conditioning on a collider variable. Annual Review of Sociology, 40, 31-53. doi:10.1146/annurev-soc-071913-043455.

Fishbein, M., & Ajzen, I. (2010). Predicting and changing behavior: The reasoned action approach. New York: Taylor & Francis.

Franc, R., & Pavlović, T. (2018). Systematic review of quantitative studies on inequality and radicalisation. DARE (725349).

Frischlich, L., Rieger, D., Hein, M., & Bente, G. (2015). Dying the right-way? Interest in and perceived persuasiveness of parochial extremist propaganda increases after mortality salience. Frontiers in Psychology, 6, 1222.

Glymour, C. (2004). The automation of discovery. Daedalus, 133(1), 69-77. doi:10.1162/001152604772746710

Grossman, M., & Tahiri, H. (2015). Community perceptions of radicalisation and violent extremism: An Australian perspective. Journal of Policing, Intelligence and Counter Terrorism, 10(1), 14-24.

Hassan, G., Brouillette-Alarie, S., Alava, S., Frau-Meigs, D., Lavoie, L., Fetiu, A., ... & Sieckelinck, S. (2018). Exposure to extremist online content could lead to violent radicalization: A systematic review of empirical evidence. International Journal of Developmental Science, 12(1-2), 71-88.

Horgan, J. (2008). From profiles to pathways and roots to routes: Perspectives from psychology on radicalization into terrorism. The ANNALS of the American Academy of Political and Social Science, 618(1), 80-94.

Johnson, N. F., Leahy, R., Restrepo, N. J., Velasquez, N., Zheng, M., Manrique, P., ... & Wuchty, S. (2019). Hidden resilience and adaptive dynamics of the global online hate ecology. Nature, 573(7773), 261-265.

Kerodal, A. G., Freilich, J. D., & Chermak, S. M. (2016). Commitment to extremist ideology: Using factor analysis to move beyond binary measures of extremism. Studies in Conflict & Terrorism, 39(7-8), 687-711.

Klausen, J., Campion, S., Needle, N., Nguyen, G., & Libretti, R. (2016). Toward a behavioral model of “homegrown” radicalization trajectories. Studies in Conflict & Terrorism, 39(1), 67-83.

Kramer, A. D., Guillory, J. E., & Hancock, J. T. (2014). Experimental evidence of massive-scale emotional contagion through social networks. Proceedings of the National Academy of Sciences, 111(24), 8788-8790.

Kruglanski, A. W., Gelfand, M. J., Bélanger, J. J., Sheveland, A., Hetiarachchi, M., & Gunaratna, R. (2014). The psychology of radicalization and deradicalization: How significance quest impacts violent extremism. Political Psychology, 35, 69-93.

LaFree, G., Jensen, M. A., James, P. A., & Safer‐Lichtenstein, A. (2018). Correlates of violent political extremism in the United States. Criminology, 56(2), 233-268.

Landers, R. N., Brusso, R. C., Cavanaugh, K. J., & Collmus, A. B. (2016). A primer on theory-driven web scraping: Automatic extraction of big data from the Internet for use in psychological research. Psychological Methods, 21(4), 475-492.

Lösel, F., King, S., Bender, D., & Jugl, I. (2018). Protective factors against extremism and violent radicalization: A systematic review of research. International Journal of Developmental Science, 12(1-2), 89-102.

Loza, W. (2011). The prevalence of the Middle-Eastern extreme ideologies among some Canadians. Journal of Interpersonal Violence, 26(7), 1388-1400.

McCrae, R. R., & Costa, P. T., Jr. (2008). The five-factor theory of personality. In O. P. John, R. W. Robins, & L. A. Pervin (Eds.), Handbook of personality: Theory and research. The Guilford Press, 159-181.

McGlashan, J., Johnstone, M., Creighton, D., de la Haye, K., & Allender, S. (2016). Quantifying a systems map: Network analysis of a childhood obesity causal loop diagram. Plos One, 11(10).

McGregor, I., Hayes, J., & Prentice, M. (2015). Motivation for aggressive religious radicalization: Goal regulation theory and a personality× threat× affordance hypothesis. Frontiers in Psychology, 6(1325), 1-18.

MacKinnon, D. P., Fairchild, A. J., & Fritz, M. (2007). Mediation analysis. Annual Review of Psychology, 58, 593-614.

McGilloway, A., Ghosh, P., & Bhui, K. (2015). A systematic review of pathways to and processes associated with radicalization and extremism amongst Muslims in Western societies. International review of psychiatry, 27(1), 39-50.

Mitts, T. (2019). From isolation to radicalization: Anti-Muslim hostility and support for ISIS in the West. American Political Science Review, 113(1), 173-194.

Moher, D., Liberati, A., Tetzlaff, J., Altman, D. G., Altman, D., Antes, G., ... & Clark, J. (2009). Preferred reporting items for systematic reviews and meta-analyses: the PRISMA statement (Chinese edition). Journal of Chinese Integrative Medicine, 7(9), 889-896.

Munn, L. (2019). Alt-right pipeline: Individual journeys to extremism online. First Monday, 24(6).

Neumann, P., & Kleinmann, S. (2013). How rigorous is radicalization research? Democracy and Security, 9(4), 360-382.

Odag, Ö., Leiser, A., & Boehnke, K. (2019). Reviewing the role of the Internet in radicalization processes. Journal for Deradicalization, 21, 261-300.

Opp, K. D. (2019). Analytical Criminology. Integrating Explanations of Crime and Deviant Behavior. Routledge.

Opp, K.-D., & Wippler, R. (Eds.) (1990). Empirischer Theorienvergleich. Erklärungen sozialen Verhaltens in Problemsituationen. [Empirical comparison of theories. Explanations of social behaviour in problem situations] Opladen: Westdeutscher Verlag.

Ozer, S., & Bertelsen, P. (2018). Capturing violent radicalization: Developing and validating scales measuring central aspects of radicalization. Scandinavian Journal of Psychology, 59(6), 653-660.

Pape, R.A. (2009) Introduction: What is new about research on terrorism. Security Studies, 18(4), 643-650.

Parekh, D., Amarasingam, A., Dawson, L., & Ruths, D. (2018). Studying jihadists on social media: A critique of data collection methodologies. Perspectives on Terrorism, 12(3), 5-23.

Pauwels, L., & Schils, N. (2016). Differential online exposure to extremist content and political violence: Testing the relative strength of social learning and competing perspectives. Terrorism and Political Violence, 28(1), 1-29.

Pauwels, L. J., & Svensson, R. (2017). How robust is the moderating effect of extremist beliefs on the relationship between self-control and violent extremism?. Crime & Delinquency, 63(8), 1000-1016.

Pawson, R. (2006). Evidence-based policy: A realist perspective. Sage.

Pearl, J. (2009). Causality: Models, reasoning, and inference. New York: Cambridge University Press.

Pearl, J., Glymour, C., & Jewell, N. P. (2016). Causal inference in statistics: A primer: Wiley.

Pearl, J., & MacKenzie, D. (2018). The book of why. New York: Basic Books.

Pelzer, R. (2018). Policing of terrorism using data from social media. European Journal for Security Research, 3(2), 163-179.

Pratt, T. C., & Cullen, F. T. (2000). The empirical status of Gottfredson and Hirschi's general theory of crime: A meta‐analysis. Criminology, 38(3), 931-964.

Pretus, C., Hamid, N., Sheikh, H., Ginges, J., Tobeña, A., Davis, R., ... & Atran, S. (2018). Neural and behavioral correlates of sacred values and vulnerability to violent extremism. Frontiers in Psychology.

R Core Team (2018). R: A language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria. Available online at

Rieger, D., Frischlich, L., & Bente, G. (2017). Propaganda in an insecure, unstructured world: How psychological uncertainty and authoritarian attitudes shape the evaluation of right-wing extremist internet propaganda. Journal of Deradicalization, 10, 203-229.

Rohrer, J. M. (2018). Thinking clearly about correlations and causation: Graphical causal models for observational data. Advances in methods and practices in psychological science, 1(1), 27-42. doi:10.1177/2515245917745629

Rowe, M., & Saif, H. (2016). Mining pro-ISIS radicalisation signals from social media users. In Tenth International AAAI Conference on Web and Social Media.

Sackett D., Rosenberg, W., Gray, J., Haynes, R., &, Richardson, WS. (1996). Evidence-based medicine: What it is and what it isn’t. British Medical Journal, 312(7023):71–72.

Sageman, M. (2014). The stagnation in terrorism research. Terrorism and Political Violence, 26(4), 565-580.

Scarcella, A., Page, R., & Furtado, V. (2016). Terrorism, radicalisation, extremism, authoritarianism and fundamentalism: A systematic review of the quality and psychometric properties of assessments. PloS one, 11(12).

Schmid, A. P. (2013). Radicalisation, de-radicalisation, counterradicalisation: A conceptual discussion and literature review. ICCT Research Paper, 97(1).

Schmid, A. P., & Forest, J. J. (2018). Research desiderata: 150 un- and under-researched topics and themes in the field of (counter-) terrorism studies–a new list. Perspectives on terrorism, 12(4), 68-76.

Shrier, I., & Platt, R. W. (2008). Reducing bias through directed acyclic graphs. BMC Medical Research Methodology, 8(1), 70.

Simon, B., Reichert, F., & Grabow, O. (2013). When dual identity becomes a liability: Identity and political radicalism among migrants. Psychological Science, 24(3), 251-257.

Slootman, M., & Tillie, J. (2006). Processes of radicalisation. Why some Amsterdam Muslims become radicals. Amsterdam: Institute for Migrations and Ethnic Studies, University of Amsterdam, Amsterdam, 1-129.

Stern, J. (2016). Radicalization to extremism and mobilization to violence: What have we learned and what can we do about it? The ANNALS of the American Academy of Political and Social Science, 668(1), 102-117.

Sweeney, M. M., & Perliger, A. (2018). Explaining the spontaneous nature of far-right violence in the United States. Perspectives on Terrorism, 12(6), 52-71.

Taylor, W. D., Johnson, G., Ault, M. K., Griffith, J. A., Rozzell, B., Connelly, S., ... & Ness, A. M. (2015). Ideological group persuasion: A within-person study of how violence, interactivity, and credibility features influence online persuasion. Computers in Human Behavior, 51, 448-460.

Tranfield, D., Denyer, D., & Palminder, S. (2003). Towards a methodology for developing evidence-informed management knowledge by means of systematic review. British Journal of Management, 14, 207-222.

Vanderweele, T. J. (2019). Principles of confounder selection. European Journal of Epidemiology, 3, 211-219. doi:10.1007/s10654-019-00494-6

Van De Wijngaert, L., Bouwman, H., & Contractor, N. (2014). A network approach toward literature review. Quality & Quantity, 48(2), 623-643.

Vahratian, A., Siega-Riz, A. M., Savitz, D. A., & Zhang, J. (2005). Maternal pre-pregnancy overweight and obesity and the risk of caesarean delivery in nulliparous women. Annals of Epidemiology, 15(7), 467-474. doi:10.1016/j.annepidem.2005.02.005

Vergani, M., Iqbal, M., Ilbahar, E., & Barton, G. (2018). The three Ps of radicalization: Push, pull and personal. A systematic scoping review of the scientific evidence about radicalization into violent extremism. Studies in Conflict & Terrorism, 1-32.

Viswesvaran, C., & Ones, D. S. (1995). Theory testing: Combining psychometric meta-analysis and structural equations modeling. Personnel Psychology, 48, 865-885.

Wasserman, S., & Faust, K. (1994). Social network analysis: Methods and applications (Vol. 8): Cambridge University Press.

Wibisono, S., Louis, W. R., & Jetten, J. (2019). A Multi-Dimensional Analysis of Religious Extremism. Frontiers in Psychology, 10, 2560. doi: 10.3389/fpsyg.2019.02560

Wolfowicz, M., Litmanovitz, Y., Weisburd, D., & Hasisi, B. (2019). A field-wide systematic review and meta-analysis of putative risk and protective factors for radicalization outcomes. Journal of Quantitative Criminology, 1-41.

Zhirkov, K., Verkuyten, M., & Weesie, J. (2014). Perceptions of world politics and support for terrorism among Muslims: Evidence from Muslim countries and Western Europe. Conflict Management and Peace Science, 31(5), 481-501.