Reexamination of the Purchasing Power Parity (PPP) under Cournot Competition

This paper reexamines the Purchasing Power Parity (PPP) in an open economy macroeconomic model with Cournot competition in the international trade of a unique good. Foreign and domestic firms have a Cournot perception of foreign and domestic markets and make separate quantity decisions for each market taking the quantity decisions of the other firm as given. In introducing the money, the balance of payments relation and the nominal exchange rate, the PPP implied by the law of one price can be reexamined. We show that the imperfect competition and symetric trade barriers are not enough to break the absolute and relative PPP. But under symmetric trade barriers, asymmetric policy and macroeconomic conditions are sufficient for the absolute PPP not to hold, while asymmetric trade barriers are enough to break it. These results are developed without calling on the role of non-tradable goods, shifts in the consumers’ tastes or technological changes, which are commonly considered as the principal factors to break the absolute and relative PPP. Conditions under which the relative PPP is not verified are discussed.