Abstract
Ecological patent registrations have been increasing in the USA steadily over time. The paper analyses trends and volatility in US ecological patents in the USA from 1975 to 1997. Germany contributed more than 10% of the total number of US ecological patents, and has been by far the strongest foreign performer. The time-varying nature of the volatility of the ecological patent share, namely the ratio of US ecological patents to total US patents, is examined using monthly data from January 1975 to December 1997. As negative and positive movements in the patent share may have differential impacts on innovative activity, and hence on volatility, both symmetric and asymmetric models of volatility are estimated. The asymmetric AR(1)-GJR(1,1) model is found to be suitable for modelling the ecological patent share in the USA.
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