Researchers increasingly conduct quantitative studies of terrorist groups, which is an important advance in the literature. However, there has been little discussion of what constitutes a “terrorist group,” regarding conceptualization or measurement. Many studies of terrorist groups do not define the term, and among those that do, definitions vary considerably. The lack of clarity leads to conceptual confusion as well as sample selection issues, which can affect inferences. To address these issues, this article offers an in-depth analysis of the term and its use. It explores definitions in the literature, and then discusses different samples used. Empirically, the article demonstrates how sample selection can affect variable values. It also shows that a non-representative sample, such as the U.S. Foreign Terrorist Organization list, can lead to inaccurate generalizations. Ultimately, I present a straightforward “inclusive” definition, and argue for its practicality. Other suggestions are made for a more effective and cohesive research program.
Phillips, Brian J. "What is a terrorist group? Conceptual issues and empirical implications." Terrorism and Political Violence 2015: 27 (2): 225-242. http://www.tandfonline.com/doi/abs/10.1080/09546553.2013.800048