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.

Many have argued that if labor income is difference stationary, the permanent income hypothesis predicts that consumption should be relatively volatile. In U.S. aggregate data, labor income is well characterized as having a unit root; however, consumption turns out to be relatively smooth. This anomaly is known as Deaton's paradox. I resolve Deaton's paradox by providing decompositions of labor income into permanent and transitory components. These preserve the univariate dynamic properties of labor income. However, when agents distinguish permanent and transitory movements in their labor income--as the rational expectations hypothesis asserts they should--the permanent income hypothesis correctly predicts the observed smoothness in consumption.