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228

CHAPTER 7. THE REAL EXCHANGE RATE

Problems

1. (Heterogeneous commodity baskets). Suppose there are two goods, both of which are internationally traded and for whom the law of one

price holds,

p1t = st + p1t, p2t = st + p2t,

where pi is the home currency price of good i, pi is the foreign currency price, and s is the nominal exchange rate, all in logarithms. Assume further that the nominal exchange rate follows a unit-root process, st = st−1 + vt where vt is a stationary process, and that foreign prices are driven by a common stochastic trend, zt

p1t = zt + ²1t p2t = zt + ²2t.

where zt = zt−1 + ut, ²it, (i = 1, 2) are stationary processes, and ut is iid with E(ut) = 0, E(u2t ) = σu2. Show that even if the price levels are

constructed as,

p

t

= φp

1t

+ (1

φ)p

,

p = φ p

+ (1

φ )p

,

 

 

 

2t

 

t

1t

 

2t

 

with φ 6= φ , that pt − (st + pt ) is a stationary process.