We model a market populated by two groups of boundedly rational agents: “newswatchers” and “momentum traders.” Each newswatcher observes some private information, but fails to extract other newswatchers’ information from prices. If information diffuses gradually across the population, prices underreact in the short run. The underreaction means that the momentum traders can profit by trendchasing. However, if they can only implement simple (i.e., univariate) strategies, their attempts at arbitrage must inevitably lead to overreaction at long horizons. In addition to providing a unified account of under- and overreactions, the model generates several other distinctive implications.

This paper investigates the dynamics in a simple present discounted value asset pricing model with heterogeneous beliefs. Agents choose from a finite set of predictors of future prices of a risky asset and revise their `beliefs' in each period in a boundedly rational way, according to a `fitness measure' such as past realized profits. Price fluctuations are thus driven by an evolutionary dynamics between different expectation schemes (`rational animal spirits'). Using a mixture of local bifurcation theory and numerical methods, we investigate possible bifurcation routes to complicated asset price dynamics. In particular, we present numerical evidence of strange, chaotic attractors when the intensity of choice to switch prediction strategies is high.

We survey the empirical literature on floating nominal exchange rates over the past decade. Exchange rates are difficult to forecast at short- to medium-term horizons. There is a bit of explanatory power to monetary models such as the Dornbusch "overshooting " theory, in the form of reaction to "news " and in forecasts at long-mn horizons. Nevertheless, at short horizons, a driftless random walk characterizes exchange rates better than standard models based on observable macroeconomic fundamentals. Unexplained large shocks to floating rates must then, logically, be due either to innovations in unobservable fundamentals, or to non-fundamental factors such as speculative bubbles. The observed difference in exchange rate and macroeconomic volatility under different nominal exchange rate regimes makes us skeptical of the first view. The theory and evidence on speculative bubbles, however, is not conclusive. We conclude with the hope that promising new studies of the microstructure of the foreign exchange

This paper develops a welfare-based model of monetary policy in an open economy. We examine the optimal monetary policy under commitment, focusing on the nature of price adjustment in determining policy. We investigate the implications of these policies for exchange-rate flexibility. The traditional approach maintains that exchange rate flexibility is desirable in the presence of real country-specific shocks that require adjustment in relative prices. However, in the light of empirical evidence on nominal price response to exchange-rate changes – specifically, that there appears to be a large degree of local-currency pricing in industrialized countries – the expenditure-switching role played by nominal exchange rates may be exaggerated in the traditional literature. In the presence of local-currency pricing, we find that the optimal monetary policy leads to a fixed exchange rate, even in the presence of country specific shocks. This is true whether monetary policy is chosen cooperatively or non-cooperatively among countries.

Using a unique data set, we study the trading behavior of foreign portfolio investors in Korea before and during the currency crisis. Different categories of investors have significant differences as well as similarities. First, non-resident institutional investors are always positive feedback traders, whereas resident investors before the crisis were negative feedback (contrarian) traders but switch to be positive feedback traders during the crisis. Second, individual investors herd significantly more than institutional investors. Non-resident (institutional as well individual) investors herd significantly more than their resident counterparts. Third, differences in the Western and Korean news coverage are correlated with differences in net selling by nonresident investors relative to resident investors.

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This paper documents that hedge funds did not exert a correcting force on stock prices during the technology bubble. Instead, they were heavily invested in technology stocks. This does not seem to be the result of unawareness of the bubble: Hedge funds captured the upturn, but, by reducing their positions in stocks that were about to decline, avoided much of the downturn. Our findings question the efficient markets notion that rational speculators always stabilize prices. They are consistent with models in which rational investors may prefer to ride bubbles because of predictable investor sentiment and limits to arbitrage.

Exchange rate regimes differ primarily by the noisiness of the exchange rate, not observable macroeconomic “fundamentals.” Fixed exchange rates are typically stable and floating exchange rates are volatile, but macro phenomena are regime-independent. Fundamentals only seem to be relevant for exchange rates at low frequencies or when inflation is high. A basic task of international finance is explaining these cross-regime differences in exchange rate volatility. The evidence suggests that a switch in exchange rate policy is accompanied by a change in market structure; macroeconomic considerations are superfluous. We formalise this observation in a non-linear model with multiple equilibria.