The Relative Importance of Permanent and Transitory Components: Identification and some Theoretical Bounds

Publication Date
Financial Markets Group Discussion Papers DP 126
Publication Authors

Much macroeconometric discussion has recently emphasized the economic significance of the size of the permanent component in GNP. Consequently, a large literature has developed that tries to estimate this magnitude--measured, essentially, as the spectral density of increments in GNP at frequency zero. This paper shows that unless the permanent component is a random walk this attention has been misplaced: in general, that quantity does not identify the magnitude of the permanent component. Further, by developing bounds on reasonable measures of this magnitude, the paper shows that a random walk specification is biased towards establishing the permanent component as important.