Mean-reversion vs. adjustment to PPP: the two regimes of exchange rate dynamics under the EMS, 1979–1998

This paper examines jointly the empirical relevance of the mean-reversion and the PPP hypotheses in the exchange rate dynamics under the EMS. Given the non-stationarity and the non-linearities characterizing the foreign exchange rate dynamics, this question is studied using a MS-ECM model: it allows a discontinuous adjustment towards the cointegration relationship. We find that the European exchange rates of the ERM members display mean-reversion towards the central parity in the credible regime, whereas they adjust to the PPP during the volatile period. The first mechanism is due to the stabilizing effect of a credible target-zone, while the second one can be explained by the realignments made in accordance with the underlying inflation rates.