A nonlinear time series model of El Niño

A smooth transition autoregressive model is estimated for the Southern Oscillation Index, an index commonly used as a measure of El Niño events. Using standard measures there is no indication of nonstationarity in the index. A logistic smooth transition autoregressive model describes the most turbulent periods in the data (these correspond to El Niño events) better than a linear autoregressive model. The estimated nonlinear model passes a battery of diagnostic tests. A generalised impulse response function indicates local instability, but as deterministic extrapolation from the estimated model converges, the nonlinear model may still be useful for forecasting the El Niño Southern Oscillation a few months ahead. © 2001 Elsevier Science Ltd

Modeling Cyclical Asymmetries in European Imports

This paper applies smooth transition models to capture the nonlinear behavior in the imports data of six major European economies and to assess whether such nonlinearities are related to business cycle asymmetries. Two classes of switch between regimes are considered: endogenously determined transition that assumes nonlinearities are generated by idiosyncratic components specific to foreign trade, and exogenous transition based on GDP growth as a more direct indicator of the cyclical state of the economy. The results support the proposition that the dynamics of imports are nonlinear. In Belgium, France, Spain, and the United Kingdom, regimes change over the business cycle, while in Germany and Italy the switch between regimes is endogenous. National characteristics play a role in defining the position of extreme regimes, the smoothness of the transition, and local dynamics within each state. Copyright International Atlantic Economic Society 2005C32, E32, F15,