The Operational Development and Empirical Testing of the Terrorist Radicalization Assessment Protocol (TRAP–18)

ABSTRACT

The Terrorist Radicalization Assessment Protocol (TRAP–18) is a structured professional judgment instrument for threat assessment of the individual terrorist. It is a rationally derived theoretical model comprising eight proximal warning behaviors and 10 distal characteristics. Empirical research on the TRAP–18 is reviewed, including both nomothetic and idiographic studies of individual terrorists in both the United States and Europe. Mean interrater reliability is 0.895 (Cohen's kappa), ranging from 0.69 to 1.0. Evidence of criterion validity has been demonstrated, including usefulness of the instrument across various extremist ideologies (jihadism, ethnic nationalism, and single-issue), and its ability to discriminate between thwarted and successful attackers. The instrument appears to advance the domain recommendations of Monahan (2012, 2016) for the risk assessment of the individual terrorist. The TRAP–18 is further discussed as a threat assessment instrument for mental health clinicians. The limitations of the current research provide direction for further studies to assess its reliability and construct, discriminant, and predictive validity.

Acknowledgments

I would like to thank all those individuals who have contributed to the past and present work on the warning behaviors and the development of the TRAP–18, including Jens Hoffmann, Angela Guldimann, David James, Jacqueline Genzman, Alasdair Goodwill, John Monahan, Paul Gill, Jessica Yakeley, Karoline Roshdi, Justine Glaz-Ocik, Nils Bockler, Gwyn Amat, Melinda Morgan, Maria Martinez, Kostas Katsavdakis, Mary Ellen O'Toole, Elmar Habermeyer, David Marxsen, Doug Craig, Craig Rempel, Lynne Bibeau, Henrik Belfrage, Tine Wobbe, Lamia Aston, Geir Olsen, Nuno Paixao, and Helene van der Meer.

Notes

¹ Jens Hoffmann, Angela Guldimann, and the author. Work on the Terrorist Radicalization Assessment Protocol (TRAP–18) continues among collaborators in the United States, Germany, Canada, and the United Kingdom, with the important help of TRAP–18 translators from other countries.

² All of these papers are available as PDF files at drreidmeloy.com.

³ This was a subsample taken from Fein and Vossekuil (1999), where data were sufficient with additional research to code for the proximal warning behaviors.

⁴ Although there are many academic, legal, and operational definitions, terrorism is herein generally defined as ideologically motivated violence against noncombatants.

⁵ There are no empirically derived cutoffs for the TRAP–18 because it is an SPJ instrument and not a psychological test. Nevertheless, the model advances the hypothesis that one proximal warning behavior is necessary for active risk management, and data indicate that all targeted violence subjects to date have exhibited warning behaviors prior to their attacks.

⁶ There is currently ongoing research by Gill (2016) to quantitatively sequence radicalization pathways using the TRAP–18 indicators. This methodology is visualizing such sequences by using state transition diagrams, the calculation of conditional probabilities, and tests for significance.

⁷ Most of these single-issue terrorists were anti-abortionists.

⁸ These are cases in which a person knowingly and intentionally provides training, expert advice, service, or personnel for terrorist endeavors (18 US Code Section 2339A).