Sample autocorrelations of nonsationary fractionally integrated series

We derive the asymptotic distribution of the sample autocor-relations of nonstationary fractionally integrated processes of order d. If d≥1, the sample autocorrelations approach their probability limit one with a rate equal to the sample size. If d<1, the rate is slower and depends on d. These findings carry over to the case of detrended series. Monte Carlo evidence and an empirical example illustrate the theoretical results.