History of the GTD

The Global Terrorism Database—or GTD—began in 2001 when researchers at the University of Maryland obtained a large database originally collected by the Pinkerton Global Intelligence Services (PGIS).

From 1970 to 1997, PGIS trained researchers—mostly retired Air Force personnel—to identify and record terrorism incidents from wire services, government reports, and major international newspapers in order to assess the risk of terrorism for their clients. With funding from the National Institute of Justice, the Maryland team finished computerizing the original Pinkerton data in December 2005, making corrections and adding additional information wherever possible. PGIS lost data for 1993 in an office move and these data have never been fully recovered.

In April 2006, the National Consortium for the Study of Terrorism and Responses to Terrorism (START), working with the Center for Terrorism and Intelligence Studies (CETIS), received additional funding from the Human Factors Division of the Department of Homeland Security (DHS) to extend the GTD beyond 1997. This effort is distinct from the original collection because CETIS analysts had to search archival sources for documented attacks, rather than recording events as they broke. Some earlier media sources are simply unavailable, undoubtedly reducing the total number of attacks that were able to be identified since 1997. In addition, efforts begun for post-1997 cases used a slightly modified definition of terrorism, with information on specific criteria for identification as a terrorist incident included for each case.

By August 2008 data collection was completed for incidents that occurred through 2007. In Fall 2008, the GTD team applied the latter terrorism-identification criteria to the earlier GTD data in order to form a single source of information on terrorist attacks, covering the entire period 1970 to 2007 (see the "Synthesis" section of Data Collection and Methodology). Beginning in Spring 2008, analysts from the Institute for the Study of Violent Groups (ISVG) at the University of New Haven began documenting terrorist attacks for START, and data on these incidents identified by ISVG will be regularly integrated into GTD after 2007.

Thus, the Global Terrorism Database is a compilation of three data collection efforts from 1970 to the present. From 1970 to 1997 the data were constructed primarily from incidents recorded in real-time over that period by PGIS using a broad-based definition of terrorism. Data from this period are updated and corrected on an ongoing basis. The data from 1998 through 2007 were primarily collected retrospectively by analysts from CETIS, with data on more recent events being collected in real-time. New criteria for collecting data were established to assure the adherence to a broad definition of terrorism and also to allow users to filter out cases that may be inappropriate for their specific research interests. Also the post-1997 data collection included more variables for each event. Finally, in 2008, analysts from ISVG began collecting data on terrorist attacks adhering to the criteria and breadth of collection since 1997 for events occurring in 2008 and beyond. Thus, users should note that differences in levels of attacks before and after 1997 may be at least partially explained by differences in data collection; researchers should adjust for these differences when modeling the data.

Because we recently applied the latter data collection criteria to the 1970-1997 data, the data now form a complete series from 1970 to the present—except for 1993. Prior to this effort, we referred to the 1970-1997 GTD as GTD1 and the data post 1997 as GTD2. Now that the data are synthesized, the database is simply referred to as GTD.