Unit roots or nonlinear stationarity in Turkish real exchange rates

Abstract

The objective of this paper is to test if Turkish real exchange rates have a linear unit root or are generated by an Exponential Smooth Transition Autoregressive Model for the post-1980 period. Using two real exchange rates, one with the USA and the other with Germany, strong evidence of nonlinear stationarity was found for the US CPI-based series but no such evidence for the DM CPI-based series. When compared with earlier results in a previous paper where the alternative of the linear unit root test was stationarity with multiple shifts in the deterministic terms, it was found that similar results were obtained for the US CPI-based series but not for the DM CPI-based one, possibly implying that the multiple shifts approach may be more appropriate for the Turkish series.

Notes

 This is the case where the shift between the regimes is still a function of y _t −  _d but the shift takes place abruptly instead of gradually.

 In actual modelling, one may prefer to make a data-based choice between the LSTAR and ESTAR models as in Sarantis (1999). He finds that, of the G-10 countries to which he applies these models, LSTAR was preferred for only three (Germany, France and Belgium); the rest was modelled using ESTAR.