Is transnational terrorism becoming more threatening? A time-series investigation

This study applies time-series techniques to investigate the current threat posed by transnational terrorist incidents. Although the number of inciden ts has dropped dramatically during the post-cold war period, transnational terrorism still presents a significant threat. In recent years, each incide nt is almost 17 percentage points more likely to result in death or injurie s. Three alternative casualties series (incidents with injuries and/or deat hs, the proportion of incidents with casualties, and incidents with deaths) are investigated. These series increased in November 1979 with the takeove r of the U.S. embassy in Tehran and again after the fourth quarter of 1991. The growth of religious terrorism appears to account for the increased sev erity of terrorist attacks since the last quarter of 1991. All three casual ties series displayed more deterministic factors than the noncasualties ser ies, which is largely random after detrending. Cycles in the aggregate inci dent series are solely attributable to the underlying casualties series.