The Department of Economics Econometrics Seminar Series presents
"Robust Estimation of ARMA Models with Near Root Cancellation"
with Richard Startz, UC Santa Barbara
Wednesday, December 5, 2012
Standard estimation of ARMA models in which the AR and MA roots nearly cancel, so that individual coefficients are only weakly identified, often produces inferential ranges for individual coefficients that give a spurious appearance of accuracy. Startz remedies this problem with a model that mixes inferential ranges from the estimated model with those of a more parsimonious model. The mixing probability is derived using Bayesian methods, but we show that the method works well in both Bayesian and frequentist setups. In particular, he shows that our mixture procedure weights standard results heavily when given data from a well-identified ARMA model (which does not exhibit near root cancellation) and weights heavily an uninformative inferential region when given data from a weakly-identified ARMA model (with near root cancellation). When applied to a well-identified process the investigator gets the “usual results,” so there is no important statistical cost to using our procedure. On the other hand, when Startz's procedure is applied to a weakly-identified process, the investigator learns that the data tell us little about the parameters—and is thus protected against making spurious inferences. He recommends that mixture models be computed routinely when inference about ARMA coefficients is of interest.
For further information, please contact Gloria Simpson, email@example.com or 949-824-5788.