Please click here if you are unable to view this page.
TOPIC:
INFERENCE IN A STATIONARY/NONSTATIONARY AUTOREGRESSIVE TIME-VARYING-PARAMETER MODEL
ABSTRACT
Autoregressive models — stationary or nonstationary — are workhorse models in econometric time series. This paper considers nonparametric estimation and inference in autoregressive (AR) models with deterministically time-varying parameters. A key feature of the proposed approach is to allow for time-varying stationarity in some time periods, time-varying nonstationarity (i.e., unit root or local-to-unit root behavior) in other periods, and smooth transitions between the two. We allow for all parameters of the model to be time-varying, not just the AR parameter. The estimation of the AR parameter at any time point is based on the local LS regression method, where the relevant initial condition is endogenous. We introduce a new method to eliminate the impact of the endogenous initial condition on the asymptotics, and obtain limit distributions after proper normalization for the AR parameter when it is unit root, local-to-unity, and stationary/stationary-like. Asymptotic properties for t-statistics are also established. These are used to construct confidence intervals for the AR parameter at any specified point in time. This confidence interval has correct uniform asymptotic coverage probability regardless of the time-varying stationarity/nonstationary behavior of the observations.