Due to a lack of available empirical data regarding terrorism, the researchers sought to code and verify a previously unavailable dataset composed of terrorist events recorded for the entire world from 1970 through 1997. This database was originally collected by the Pinkerton Corporation's Global Intelligence Service (PGIS). Throughout the data collection period PGIS data collection employed a broad definition of terrorism: the threatened or actual use of illegal force and violence to attain a political, economic, religious, or social goal through fear, coercion, or intimidation. The data include "terrorist groups" identified as specific named groups as well as generic groupings like "rebels" or "student protesters." The PGIS database was designed to document every known terrorist event, domestic and international, across countries and time and allows examination of the total number of different types of terrorist events by specific date and geographical region. The data collection and analysis is two-pronged. First, the researchers sought to reliably enter the PGIS data. Second, the researchers continue to assess the validity of the PGIS data and how valid they are as a measure of terrorism by comparing it to other sources, by internally checking records, and by continually examining the database.
To develop the original Global Terrorism Database (GTD1) [GLOBAL TERRORISM DATABASE, 1970-1997, (ICPSR 4586)], the researchers arranged with PGIS to move 58 boxes of original hard copies of the PGIS terrorism database to a secure location at the University of Maryland. Once the data were transferred the researchers designed a system for accurately encoding the data. A large computer lab with personal computers for data entry was not a viable option so a Web-based data entry system was developed by computer experts at the University of Maryland to allow a very large number of students to work on the database, using their own equipment, on a flexible schedule. To reduce data entry errors, the data entry interface was designed to match the design of the generic incident card used by PGIS in their coding. This method had the advantage of giving the researchers a good deal of control over the data entry process and a computerized record of the time expended by all of the data coders. Therefore the researchers could easily verify individual coding records for accuracy. Second, once the database codebook and data entry interface was developed, pretesting of both the codebook and the interface was conducted to look for data entry problems. Pretesting identified an array of problems with both the data entry codebook and the Web-based system that was employed to record data. Most of these problems involved clarification of the data entry codebook language, such that data entry rules became increasingly detailed and specific. For example, the researchers created rules for using the value "unknown." In the case of fields indicating the number of persons killed and injured in an event, data entry rules stated that "unknown" was to be chosen only if the field stated "unknown" on the data card. If the field was blank on the data card, it was assumed that the number killed or injured was zero. In addition, automatic entry fields were created in the Web-based interface to be automatically applied under specific circumstances. For instance, if the event type was entered as a bombing, and the bombing was entered as successful, then the field indicating that damages were incurred was automatically activated by the interface (i.e. the damages checkbox was checked). If an event was entered as a successful kidnapping, then the checkbox indicating that persons were kidnapped in the course of the event was automatically checked. These revisions and additions to the codebook and interface were all made in the interest of increasing data entry reliability while decreasing data entry error. Third, once the researchers were confident in the quality of the data entry procedures, they developed and implemented data entry training procedures. An extensive training manual was added to the data entry codebook for this purpose and a full-day training session for an original group of approximately 70 undergraduate coders was conducted. Over time, training sessions were added as new students joined the project. Finally, once data entry began, the researchers faced the ongoing process of data verification. The original plan was to verify a randomly selected 10 percent of the total cases in the sample. Over the life of the grant until the creation of the database thus far, the project had reached a verification rate of nearly 50 percent. Project members continue to work to consolidate the group list by combining cases where one group uses multiple names or various alternative name spellings.
In order to develop the Global Terrorism Database 1.1 (GTD1.1), the research team supplemented the original PGIS data by incorporating incidents found in other data sources that were overlooked by PGIS. For several countries in the data, cases have been added, deleted, or corrected compared to the first release of the Global Terrorism Database (GTD1) [GLOBAL TERRORISMDATABASE, 1970-1997, (ICPSR 4586)] based on additional coding and investigation. This process is ongoing and is the primary reason that the GTD is an evolving data source. Other data sources include the Conflict Archive on the Internet, the Australian Turkish Media Group, Armenian Terrorism: the past, present, the prospects, by Francis Hyland, the National Abortion Federation, and the "Further Submissions and Responses by the ANC to Questions Raised by the Commission for Truth and Reconciliation 12 May 1997". Data in the GTD1.1 contain 61,637 events.
The Global Terrorism Database (GTD1) [GLOBAL TERRORISM DATABASE, 1970-1997, (ICPSR 4586)] was designed to document every known terrorist event across countries and time. The PGIS data include political as well as religious, economic, and social acts of terrorism. Because the PGIS data were collected by a private business rather than a government entity, the data collectors were under no pressure to exclude some terrorist acts because of political considerations. The database also includes instances of both domestic and international terrorism starting from 1970. The PGIS data collection efforts applied a similar data collection strategy for a 28-year period. PGIS trained their employees to identify and code terrorism incidents from a variety of sources, including wire services (especially Reuters and the Foreign Broadcast Information Service), United States State Department reports, other United States and foreign government reports, United States and foreign newspapers, information provided by PGIS offices around the world, occasional inputs from such special interests as organized political opposition groups, and data furnished by PGIS clients and other individuals in both official and private capacities. Based on coding rules originally developed in 1970, the persons responsible for collecting the PGIS database sought to exclude criminal acts that appeared to be devoid of any political or ideological motivation as well as acts arising from open combat between opposing armed forces, both regular and irregular. The data coders also excluded actions taken by governments in the legitimate exercise of their authority, even when such actions were denounced by domestic and/or foreign critics as acts of "state terrorism." However, they included violent acts that were not officially sanctioned by the government, even in cases where many observers believed that the government was openly tolerating the violent actions. The database includes potential media bias and misinformation, lacks information beyond incident-specific details alone, and is missing data for the year 1993 (lost by PGIS in an office move).
In order to develop the Global Terrorism Database 1.1 (GTD1.1), the research team supplemented the original PGIS data by incorporating incidents found in other data sources that were overlooked by PGIS including special interest archives, nonprofit media response organizations, professional associations, and various print and electronic publications.
All known terrorist events that occurred in the world from 1970 through 1997.
The data source for the original Global Terrorism Database (GTD1) [GLOBAL TERRORISM DATABASE, 1970-1997, (ICPSR 4586)] was the hard copy data cards compiled by the Pinkerton Global Intelligence Service (PGIS). In order to develop the Global Terrorism Database 1.1 (GTD1.1), the research team supplemented the original PGIS data with the following additional data sources: the Conflict Archive on the Internet, the Australian Turkish Media Group, Armenian Terrorism: the past, present, the prospects, by Francis Hyland, the National Abortion Federation, and the "Further Submissions and Responses by the ANC to Questions Raised by the Commission for Truth and Reconciliation 12 May 1997".
Variables provide group name (up to three groups), type of terrorist incident (assassination, bombing, facility attack, hijacking, kidnapping, maiming, assault, mass disruption, or arson), incident date (year, month, day of month), region, country, state in the United States (if applicable), city, whether the incident was just outside of the city, the type of target (business, government, police, military, abortion related, airport and airplanes, diplomatic, educational institution, food or water supply, journalists and media, maritime, NGO, private citizens and property, religious figures/institutions, terrorists, tourists, transportation, utilities, criminal, scientist, sports related, other, and unknown), the identity and nationality of the target (up to three targets), type of weapons used (up to three weapon types), whether the incident was considered a success, and whether there was some damage. Further variables classify the total number killed (persons, terrorists) and total number wounded (persons, terrorists). Further variables provide information about kidnappings and hostages (total, United States nationals), total number of days and hours held, and amount of ransom demanded and amount paid (overall, United States nationals). Variables also record information about hijackings (where diverted, status of victims, and number of victims released). Another variable also provides the number of incidents that the case represents.