Nonlinear Purchasing Power Parity under the Gold Standard

Hegwood and Papell (2002) conclude on the basis of analysis in a linear framework that long-run purchasing power parity (PPP) does not hold for 16 real exchange rate series, which were analyzed in Diebold, Husted, and Rush (1991) for the period 1792-1913 under the Gold Standard. Rather, PPP deviations are mean-reverting to a changing equilibrium-a quasi PPP (QPPP) theory. We analyze the real exchange rate adjustment mechanism for their data set assuming a nonlinear adjustment process allowing for both a constant and a mean shifting equilibrium. Our results confirm that real exchange rates at that time were stationary, symmetric, nonlinear processes that revert to a nonconstant equilibrium rate. Speeds of adjustment were much quicker when breaks were allowed.