Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
9555413 | Journal of Econometrics | 2005 | 26 Pages |
Abstract
We derive a method to link exactly the autocovariance functions of two arbitrary instantaneous transformations of a time series. For example, this is useful when one wants to derive the autocovariance of the logarithm of a series from the known autocovariance of the original series and, more generally, when one wishes to describe the time-series effects of applying a nonlinear transformation to a process whose properties are known. As an illustration, we provide two corollaries and three examples. The first corollary is on the commonly used logarithmic transformation, and is applied to a geometric auto-regressive (AR) process, as well as to a positive moving-average (MA) process. The second corollary is on the tanâ1(·) transformation which will turn possibly unstable series into stable ones. As an illustration, we obtain the autocovariance function of the tanâ1(·) of an arithmetic AR process. This filter, while always producing a bounded process, preserves the stability/instability distinction of the original series, a feature that can be turned to an advantage in the design of tests. We then present a probabilistic interpretation of the main features of the new autocovariance function. We also provide a mathematical lemma on a general integral which is of independent interest.
Related Topics
Physical Sciences and Engineering
Mathematics
Statistics and Probability
Authors
Karim M. Abadir, Gabriel Talmain,