In the purchasing power parity (PPP) literature, it was traditionally
assumed that transaction costs were incompatible with strong PPP or, alternatively,
stationary real exchange rates (RERs). In recent years, however, the
role of transaction costs has been reformulated so that they are viewed as
leading to nonlinearities in RER adjustment by creating a no-arbitrage band
around PPP equilibrium. A growing literature has emerged, which models
nonlinearities in RER adjustment as either smooth transition autoregressive
(STAR) or threshold autoregressive (TAR) processes.1 In the TAR specification
adopted below, RERs are conceptualised as exhibiting persistent
dynamics within a no-arbitrage band of small deviations from equilibrium
but mean reverting behaviour in the outer bands where large deviations trigger
profitable arbitrage activity.
This paper seeks to provide a reconciliation between transaction costs and
long-run PPP in a nonlinear framework. A TAR model is chosen since it squares