SUMMARYWe use spectral analysis to provide evidence that cycles have characterized the following time series: all terrorist events, skyjackings, kidnappings, barricade and hostage‐taking, and all events not involving hostages. The series for all events had a periodicity of 28 months, while skyjackings had two significant periodicities ‐ 4.1 months and 28 months. Only a single significant periodicity was associated with barricade and hostage events and kidnappings ‐72 months and 48 months, respectively. We also found that nonlinear trends best represented four of the five series. Cross‐spectral analysis was then applied to the six possible pairs of series; each pair displays from three to nine statistically significant coherencies. Moreover, we discovered evidence of orthogonality for five of the six pairs studied. This evidence suggests that terrorists substitute between related events; this substitution primarily showed up in the short run.

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Travel destinationscommonly levy hotel cent.' In August 1984, the average hotel room t=es to finance services demanded room tax rate in 45 U.S. cities with room by tourists and residents. Evidence to date taxes was about 7 percent (Mak, 1988). A on the effects of a hotel room tax has cen-similar survey of 242 U.S. visitor conventered on ex ante analyses of the incidence tion bureaus found that the average hotel of a hotel room tax and its effect on the room tax rate in January 1990 was nearly demand for travel and vacation goods. In 10 percent [Hiemstra and Ismail, (1990, this paper we employ interrupted time se-p. 4)]. With the enactment of a 5 percent ries analysis to estimate ex post the impact hotel room tax by the State of New York of a hotel room tax on real net hotel reu-in June 1990, New York City currently enues by analyzing that time series before has the highest hotel room occupancy tax in the U.S. at 19.25 percent plus $2 on and after the imposition of the tax, We find every room priced at $100 or more. 2 that the tax had a negligible effect on real The popularity of the hotel room tax hotel revenues. stems from the widely held perception that its burden is largely borne by tourists Introduction rather than residents, with little negative

This paper examines the sequence of optimal extraction of nonrenewable resources in the presence of multiple demands. We provide conditions under which extraction of a nonrenewable resource may be discontinuous over the course of its depletion.

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