ABSTRACT
In economic time series, we frequently face long-lasting increasing or
decreasing trends. In this chapter, we initially consider a polynomial re-
gression model to analyze time series with such tendencies. Secondly,
we shall introduce a trend model to estimate a complicated trend that we
cannot express in terms of a simple parametric model such as a poly-
nomial or trigonometric regression model. The trend component model
treated in this chapter, representing stochastic changes of parameters,
forms a framework for modeling various types of nonstationary time se-
ries that will be introduced in succeeding chapters.
