Cycles and Substitutions in Terrorist Activities: A Spectral Approach.

This paper uses spectral analysis to provide evidence that cycles have characterized the following time series: all ter rorist events, skyjackings, kidnappings, barricade and hostage taking and all events not involving hostages. The series for all events ha d a periodicity of 28 months, while skyjackings had two significant p eriodicities-4.1 months and 28 months. Only a single significant pero dicity was associated with barricade and hostage events and kidnappin gs-72 months and 48 months, respectively. Cross-spectral tests sugges t that terrorists substitute between related events (e.g., kidnapping s and skyjackings); but this substitution primarily showed up in the short run. Copyright 1987 by WWZ and Helbing & Lichtenhahn Verlag AG