# POTENTIAL PITFALLS FOR THE PURCHASING-POWER-PARITY PUZZLE? SAMPLING AND SPECIFICATION BIASES IN MEAN-REVERSION TESTS OF THE LAW OF ONE PRICE

Article Abstract:

The PPP puzzle is based on empirical evidence that international price differences for individual goods (LOOP) or baskets of goods (PPP) appear highly persistent or even nonstationary. The present consensus is these price differences have a half-life that is of the order of five years at best, and infinity at worst. This seems unreasonable in a world where transportation and transaction costs appear so low as to encourage arbitrage and the convergence of price gaps over much shorter horizons, typically days or weeks. However, current empirics rely on a particular choice of methodology, involving (i) relatively low-frequency monthly, quarterly, or annual data, and (ii) a linear model specification. In fact, these methodological choices are not innocent, and they can be shown to bias analysis towards findings of slow convergence and a random walk. Intuitively, if we suspect that the actual adjustment horizon is of the order of days, then monthly and annual data cannot be expected to reveal it. If we suspect arbitrage costs are high enough to produce a substantial "band of inaction," then a linear model will fail to support convergence if the process spends considerable time random-walking in that band. Thus, when testing for PPP or LOOP, model specification and data sampling should not proceed without consideration of the actual institutional context and logistical framework of markets. KEYWORDS: Purchasing power parity, law of one price, mean reversion, temporal aggregation, threshold auto-regression, half-life.

Publication Name: Econometrica

Subject: Mathematics

ISSN: 0012-9682

Year: 2001

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# COSTLY BARGAINING AND RENEGOTIATION

Article Abstract:

We identify the inefficiencies that arise when negotiation between two parties takes place in the presence of transaction costs. First, for some values of these costs it is efficient to reach an agreement but the unique equilibrium outcome is one in which agreement is never reached. Secondly, even when there are equilibria in which an agreement is reached, we find that the model always has an equilibrium in which agreement is never reached, as well as equilibria in which agreement is delayed for an arbitrary length of time. Finally, the only way in which the parties can reach an agreement in equilibrium is by using inefficient punishments for (some of) the opponent's deviations. We argue that this implies that, when the parties are given the opportunity to renegotiate out of these inefficiencies, the only equilibrium outcome that survives is the one in which agreement is never reached, regardless of the value of the transaction costs. KEYWORDS: Optional bargaining costs, inefficient bargaining outcomes, renegotiation, imperfect recall.

Publication Name: Econometrica

Subject: Mathematics

ISSN: 0012-9682

Year: 2001

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