Do Significant Terrorist Attacks Increase the Risk of Further Attacks?

Initial Observations from a Statistical Analysis of Terrorist Attacks in the United States and Europe from 1970 to 2013

by Brian Michael Jenkins, Henry H. Willis, Bing Han

Download Free Electronic Document

Full Document

FormatFile SizeNotes
PDF file 0.1 MB

Use Adobe Acrobat Reader version 10 or higher for the best experience.

هل يزيد وقوع الهجمات الإرهابية الكبرى من احتمالات حدوث مزيد من الهجمات؟

Arabic language version

FormatFile SizeNotes
PDF file 0.2 MB

Use Adobe Acrobat Reader version 10 or higher for the best experience.

Major terrorist events in the United States and Europe generate fear among the public and prompt swifter responses from public officials, reflecting a belief that terrorist attacks occur in clusters. If there is one attack, the concern is that others will soon follow. That presumption leads to two analytical questions: Does a significant terrorist attack somehow inspire other terrorist attacks, and can terrorist attacks be anticipated statistically? To answer these questions, RAND researchers examine the historical record of terrorism in the United States and Europe between 1970 and the end of 2013.

Using the Global Terrorism Database, the researchers find an absence of clustering for terrorist events around trigger events since 1994, no increases in terrorism on significant dates, and a decline of terrorism in the West since the 1970s, suggesting that the threat of terrorism should not affect individuals' behavior and decisions in the United States and Western Europe — not even in the wake of a significant terrorist event. However, heightened security may be justified. It may enable authorities to respond quickly to increased reports of suspicious activity and hoaxes that terrorist events inspire. Increased police presence also permits authorities to diagnose and intervene more rapidly if there are further incidents. Moreover, temporary security increases may be warranted as a precautionary measure, even if only to reassure an alarmed public that it is safe.

This research was conducted within the RAND Homeland Security and Defense Center (HSDC), a joint center of two research divisions: RAND Justice, Infrastructure, and Environment and the RAND National Security Research Division.

This commentary is part of the RAND Corporation Expert insight series. RAND Expert Insights present perspectives on timely policy issues. All RAND Expert Insights undergo peer review to ensure high standards for quality and objectivity.

This document and trademark(s) contained herein are protected by law. This representation of RAND intellectual property is provided for noncommercial use only. Unauthorized posting of this publication online is prohibited; linking directly to this product page is encouraged. Permission is required from RAND to reproduce, or reuse in another form, any of its research documents for commercial purposes. For information on reprint and reuse permissions, please visit www.rand.org/pubs/permissions.

The RAND Corporation is a nonprofit institution that helps improve policy and decisionmaking through research and analysis. RAND's publications do not necessarily reflect the opinions of its research clients and sponsors.