Linear and Nonlinear Attractors in Purchasing Power Parity

In an examination of the PPP hypothesis over the period 1973-2014 strong evidence is found for nonlinearity, not only in the adjustment process towards equilibrium but also in the long-run relation itself. Because of the use of a data sample with a long span we also found evidence for PPP, even if it is represented by a model with linear adjustment to a linear attractor, although adjustment towards long-run equilibrium is faster when a nonlinear attractor is used. Perhaps a controversial finding is that it may be always possible to find a nonlinear attractor in the form of a high order polynomial that produces stationary residuals, implying the validity of PPP.