A time‐series analysis of transnational terrorism: Trends and cycles

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Abstract
Spectral analysis is applied to transnational terrorist time series involving all incidents, hostage incidents, bombings, assassinations, and threats and hoaxes during 1970–1989. Cycles characterize all of the series: Cycles of 7.2 quarters periodicity were found for bombings and the total of all incidents; cycles of 18 quarters were found for hostage events, all incidents, and assassinations; and cycles of 3.6 quarters were found for threats and hoaxes. Logistical complexity was positively related to the length of the cycle. Linear trend was associated with hostage events and total events, while nonlinear trend was associated with assassinations, and threats and hoaxes. Bombings showed no trend. Bombings, total incidents, and hostage events displayed stationary series due to the absence of a unit root. Assassinations and threats were nonstationary but not cointegrated. Given the regularity of cycles and the trend components uncovered, there is a clear need to develop a theoretical framework capable of explaining these cycles and trends.