Person:

Mankiw, N

Fluctuations in real GNP have traditionally been viewed as transitory deviations from a deterministic time trend. The purpose of this paper is to review some of the recent developments that have led to a new view of output fluctuations and then to provide some additional evidence. Using post-war quarterly data, it is hard to reject the view that real GNP is as persistent as a random walk with drift.We also consider the hypothesis that the recent finding of persistence are due to the failure to distinguish the business cycle from other fluctuations in real GNP. We use the measured unemployment rate to decompose output fluctuations. We find no evidence for the view that business cycle fluctuations are more quickly trend-reverting.

This paper presents new evidence on the persistence of fluctuations in real GNP. We estimate two measures of persistence nonparametrically using post-war quarterly data from Canada, France, Germany, Italy, Japan, the United Kingdom, and the United States. We compare these estimates with Monte Carlo results from various AR(2) processes. For six out of seven countries, the point estimates indicate that a 1% shock to output should change the long-run unvariate forecast of output by well over 1%. Low-order ARMA models yield similar conclusions. Finally, we examine the persistence in relative outputs of different countries.

This article reexamines the consistency of the permanent-income hypothesis with aggregate postwar U.S. data. The permanent-income hypothesis is nested within a more general model in which a fraction of income accrues to individuals who consume their current income rather than their permanent income. This fraction is estimated to be about 50%, indicating a substantial departure from the permanent-income hypothesis. Our results cannot be easily explained by time aggregation or small-sample bias, by changes in the real interest rate, or by nonseparabilities in the utility function of consumers.

According to the conventional view of the business cycle, fluctuations in output represent temporary deviations from trend. The purpose of this paper is to question this conventional view. If fluctuations in output are dominated by temporary deviations from the natural rate of output, then an unexpected change in output today should not substantially change one's forecast of output in, say, five or ten years. Our examination of quarterly postwar United States data leads us to be skeptical about this implication. The data suggest that an unexpected change in real GNP of 1 percent should change one's forecast by over 1 percent over a long horizon.