Selection and estimation of component models for seasonal time series

We present a method for investigating the evolution of trend and seasonalit y in an observed time series. A general model is fitted to a residual spect rum, using components to represent the seasonality. We show graphically how well the fitted spectrum captures the evidence for evolving seasonality as sociated with the different seasonal frequencies. We apply the method to mo del two time series and illustrate the resulting forecasts and seasonal adj ustment for one series. Copyright (C) 2000 John Wiley & Sons, Ltd.