© 1982 by Biometrika Trust
The Cramér-Rao bound and robust M-estimates for autoregressions
Department of Statistics, University of Washington Seattle, Washington, U.S.A.
A Cramér-Rao lower bound is computed for estimates of the location, innovations scale and autoregressive parameters for a finite-variance pth-order autoregression. The implication of the bound is that the usual least-squares estimates of all of these parameters have asymptotically the same lack of efficieney robustness toward heavy-tailed innovations distributions as does the sample mean for estimating location. On the other hand, autoregression analogues of Huber's regression M-estimates, with the location estimate obtained from the intercept and autoregressive parameter estimates, are shown to be efficiency robust. The location estimate is also shown to be minimax robust.
Key Words: Austoregression Cramér-Rao bound Efficiency robustness Information matrix Innovations M-estimate Minimax robustness Qualitative robustness Robust estimation Time series