Government intervention in the financial market through its own trading fundamentally changes the market’s structure, function, and outcome. I develop a general equilibrium framework to study the impact of government trading on investor welfare. I show that with incompleteness and information asymmetry, the market equilibrium is in general suboptimal, and government intervention can potentially improve investor welfare even with no additional information. However, the actual welfare impact of government intervention is sensitive to the details of the economy and the policy design. Popular policy targets such as price stability, market liquidity, and informational efficiency can have different welfare implications.

A model of competitive stock trading is developed in which investors are heterogeneous in their information and private investment opportunities and rationally trade for both informational and noninformational motives. I examine the link between the nature of heterogeneity among investors and the behavior of trading volume and its relation to price dynamics. It is found that volume is positively correlated with absolute changes in prices and dividends. I show that informational trading and noninformational trading lead to different dynamic relations between trading volume and stock returns.

[We analyze how asymmetric information and imperfect competition affect liquidity and asset prices. Our model has three periods: Agents are identical in the first, become heterogeneous and trade in the second, and consume asset payoffs in the third. We show that asymmetric information in the second period raises ex ante expected asset returns in the first, comparing both to the case where all private signals are made public and to that where private signals are not observed. Imperfect competition can instead lower expected returns. Each imperfection can move common measures of illiquidity in opposite directions.]

[In this paper, we develop an equilibrium model for stock market liquidity and its impact on asset prices when constant market presence is costly. We show that even when agents' trading needs are perfectly matched, costly market presence prevents them from synchronizing their trades and hence gives rise to endogenous order imbalances and the need for liquidity. Moreover, the endogenous liquidity need, when it occurs, is characterized by excessive selling of significant magnitudes. Such liquidity-driven selling leads to market crashes in the absence of any aggregate shocks. Finally, we show that illiquidity in the market leads to high expected returns, negative and asymmetric return serial correlation, and a positive relation between trading volume and future returns. We also propose new measures of liquidity based on its asymmetric impact on prices and demonstrate a negative relation between these measures and expected stock returns.]

[This article develops a multiperiod rational expectations model of stock trading in which investors have differential information concerning the underlying value of the stock. Investors trade competitively in the stock market based on their private information and the information revealed by the market-clearing prices, as well as other public news. We examine how trading volume is related to the information flow in the market and how investors' trading reveals their private information.]

[This article studies the central role of the credit market. We show that the credit market facilitates optimal risk sharing by allowing less risk-averse investors to take on levered positions and consume more risk. The equilibrium amount behaves procyclically when aggregate consumption is low but countercyclically when it is high. The varying size of the credit market modifies the amount of risk sharing, which in turn influences asset prices such as expected stock returns, stock return volatility, and the term structure of interest rates. Our article provides a frictionless benchmark for the role and the behavior of the credit market.]

We examine the implications of portfolio theory for the cross-sectional behavior of equity trading volume. Two-fund separation theorems suggest a natural definition for trading activity: share turnover. If two-fund separation holds, share turnover must be identical for all securities. If (K + 1)-fund separation holds, we show that turnover satisfies an approximately linear K-factor structure. These implications are examined empirically using individual weekly turnover data for NYSE and AMEX securities from 1962 to 1996. We find strong evidence against two-fund separation, and a principal-components decomposition suggests that turnover is well approximated by a two-factor linear model.

This paper presents a dynamic asset-pricing model under asymmetric information. Investors have different information concerning the future growth rate of dividends. They rationally extract information from prices as well as dividends and maximize their expected utility. The model has a closed-form solution to the rational expectations equilibrium. We find that existence of uninformed investors increases the risk premium. Supply shocks can affect the risk premium only under asymmetric information. Information asymmetry among investors can increase price volatility and negative autocorrelation in returns. Less-informed investors may rztionally behave like price chasers.

This paper presents an equilibrium model of the term structure of interest rates when investors have heterogeneous preferences. The basic model considers a pure exchange economy of two classes of investors with different (but constant) relative risk aversion and gives closed-form solutions to bond prices. I use the model to examine the effect of preference heterogeneity on the behavior of bond yields. The model is also extended to cases of more than two classes of investors.

The predictability of an asset's returns will affect the prices of options on that asset, even though predictability is typically induced by the drift, which does not enter the option pricing formula. For discretely sampled data, predictability is linked to the parameters that do enter the option pricing formula. The authors construct an adjustment for predictability to the Black-Scholes formula and show that this adjustment can be important even for small levels of predictability, especially for longer maturity options. They propose several continuous-time linear diffusion processes that can capture broader forms of predictability and provide numerical examples that illustrate their importance for pricing options.