The State of Science Regarding Membership in Terrorist Organizations  and Perpetration of Terrorist Attacks

by Sarah L. Desmarais, Joseph Simons-Rudolph, Christine Shahan Brugh, Eileen Schilling, & Chad Hoggan

North Carolina State University


One strategy in the fight against terrorism involves identifying individuals who are at heightened risk of joining terrorist organizations or perpetrating terrorist attacks. Success of this counterterrorism strategy will depend upon knowledge of the factors that increase risk for these outcomes. To date, the intelligence community has a served as a primary source of information on terrorist organizations and activity. However, hundreds of scientific papers have been written on the topic and may offer important insights into risk factors for terrorism. These largely academic endeavors have been diverse in their foci, approach, and findings. As such, there is a need to summarize the state of science regarding membership in terrorist organizations and perpetration of terrorist attacks towards the goal of informing counterterrorism strategy.


The purpose of this study was to conduct a systematic review of the published and unpublished

scientific literature regarding factors associated with joining terrorist organizations or perpetrating terrorist attacks. Our primary research aims were to: 1) describe the characteristics

of the scientific literature on risk factors for terrorism; and 2) to identify individual and environmental factors that are associated with membership in terrorist organizations and perpetration of terrorist attacks. We additionally explored the evidence supporting factors associated with the process of radicalization, including motivation and process.


Records were identified through searches of six abstracting and indexing databases using the following combinations of search terms: (a) terror* member*, (b) terror* affiliat*, (c) terror* radical*, and (d) predict* terror*. Inclusion criteria were: (a) discussed the prediction of terrorism; addressed variables related to joining terrorist organizations or perpetrating terrorist attacks; reported in peer-review journals, dissertations, theses, conference presentations, government reports, or book chapters; (d) written in English (or reliable translation); and (e) produced between 1990 and 2015. We reviewed the reference sections of articles selected for inclusion for records that were not identified through these search strategies. In total, 205 articles met our inclusion criteria. Articles were coded by two researchers using a coding scheme; a subset of 19 articles were coded by both to establish inter-rater agreement.

Overview of Findings

Findings of our systematic review revealed a growth in scientific interest in terrorism over time: more than three-quarters of the articles were produced in the last 10 years. More than half were produced by authors in the United States. Across various aspects of terrorism (such as ideology, specific organizations, types of terrorists, or types of attacks), articles rarely specified the focus of their investigation. Instead, articles often treated terrorism as one unitary or homogenous construct. Most articles discussed theoretical perspectives, critiques, or case studies. The vast majority (81%) cited findings reported in other articles as their data source. There were just 50 articles that presented results of new empirical research.

Results of the 50 empirical articles were most frequently descriptive in nature, presenting the frequencies of various characteristics amongst a group of known terrorists. A handful of articles statistically compared characteristics between known groups of terrorists; for instance, comparing level of education or prevalence of criminal histories amongst one group of terrorists versus another. Only six articles presented findings of statistical comparisons between a group of known terrorists and a group of non-terrorists. As a result, empirical evidence of variables that discriminate between terrorists and non-terrorists is limited.

Analysis of the results reported in the empirical articles revealed nine variables with at least some evidence supporting for their relevance to terrorism. These include: age, socioeconomic status, prior arrest, education, employment, relationship status, having a grievance (political or personal), specific geographic region, and type of geographic area (i.e., urban or rural). Young age, low socioeconomic status, at least high school education, and unemployment showed statistically significant associations with terrorism outcomes when comparisons were conducted between known terrorists and non-terrorists. Findings also suggest that a triggering event, such as a major personal loss, may act as the impetus for radicalization. Additional individual characteristics, including country of birth, being Muslim, military experience, foreign travel history, family or friend in a terrorist or extremist organization, and environmental characteristics, including income inequality, and media and government influences, were prevalent among the samples of known terrorists and merit further investigation as potential risk factors. Given the limitations of the research, however, there is not enough empirical evidence to conclude that any of these variables are indeed risk factors for terrorism.


Findings of our review have implications for research and counterterrorism strategy. With respect to research, the small number of comparison studies is a critical limitation of the scientific literature. For a certain characteristic to be established as a risk factor for terrorism, it must be shown that the characteristic is statistically associated with terrorism and that it precedes (temporally) terrorist activity. It is only possible to show this statistical association through longitudinal studies that compare characteristics of terrorists and non-terrorists. As such, the conduct of comparative studies of individuals or groups over time is an urgent direction for future research. Further, articles typically focused on the independent effects of individual or environmental factors; yet, risk for terrorism most likely reflects an interaction of factors within and across these levels. We also were limited to examination of findings reported in the scientific literature to date. As new terrorist organizations emerge, there will be a need to revisit the relevance of established and refuted risk factors to these new threats.

With respect to counterterrorism strategy, our findings suggest that some presumed risk factors are not related to terrorism at all or in the anticipated direction. Take country of birth, for example; the one statistical comparison found that homegrown terrorists were more likely to be born in the United States than were their non-terrorist counterparts. Thus, domestic (as opposed to foreign) country of birth appears to be a risk factor for terrorism. Several other characteristics, such as religious conversion, being Muslim, and foreign travel history, were not statistically associated with terrorism outcomes, when examined. Counterterrorism strategies focused on these presumed risk factors are likely to be ineffective. Focusing on these factors also may increase risk for terrorism by contributing to a sense of persecution or discrimination that may (further) radicalize the individual or group and ‘justify’ terrorist activity. Finally, counterterrorism strategy that focuses on the presence of certain risk factors in and of themselves is likely to be of limited value without information on the social or political context and vice versa. To demonstrate, focusing on young age, male gender, and being single as risk factors for terrorism will not help discriminate amongst a pool of potential targets who are all young, single men.  The lead author may be reached at .

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