Time-dependence or instability in the threshold so far in the literature may be implemented through either a change-point mechanism or a function of candidate variables. Bessec (2003) proposes a Self-Exciting Threshold Autoregressive (SETAR) model with time-varying thresholds using a one-time break where the change point is not estimated but corresponds to the time of the change in the official margins, and nds that the data do not reject the time-varying threshold specication.