Knowledge that Transforms

We evaluate the performance of models for the covariance structure of stock returns, focusing on their use for optimal portfolio selection. We compare the models' forecasts of future covariances and the optimized portfolios' out-of-sample performance. A few factors capture the general covariance structure. Portfolio optimization helps for risk control, and a three-factor model is adequate for selecting the minimum-variance portfolio. Under a tracking error volatility criterion, which is widely used in practice, larger differences emerge across the models. In general more factors are necessary when the objective is to minimize tracking error volatility.

The dynamics of the unobservable short rate are frequently estimated directly using a proxy. We examine the biases resulting from this practice (the “proxy problem”). Analytic results show that the proxy problem is not economically significant for single-factor affine models. In the two-factor affine model of Longstaff and Schwartz (1992), the proxy problem is only economically significant for pricing discount bonds with maturities of more than five years. We also describe two different numerical procedures for assessing the magnitude of the proxy problem in a general interest rate model. When applied to a nonlinear single-factor model, they suggest that the proxy problem can be economically significant.

Analysis of absence of arbitrage normally ignores payoffs in states to which the agent assigns zero probability. We extend the fundamental theorem of asset pricing to the case of “no empty promises” in which the agent cannot promise arbitrarily large payments in some states. There is a superpositive pricing rule that can assign positive price to claims in zero probability states important to the market as well as assigning positive prices to claims in the states of positive probability. With continuous information arrival, no empty promises can be enforced by shutting down the agent's subsequent investments once wealth hits zero.

http://deepblue.lib.umich.edu/bitstream/2027.42/39533/3/wp143.pdf

We study the precursors and outcomes of refocusing episodes by 107 diversified firms that were not taken over between 1984 and 1993. These firms had more value-reducing diversification policies than diversified firms that did not refocus. However, major disciplinary or incentive-altering events (including management turnover, outside shareholder pressure, changes in management compensation, and financial distress) usually occurred before refocusing took place. The cumulative abnormal returns over a firm's refocusing-related announcements averaged 7.3% and were significantly related to the amount of value reduction associated with the refocuser's diversification policy.

This paper investigates the distribution of equity ownership between entrenched corporate insiders and dispersed outsiders when management has the ability to divert or manipulate the cash flows and when it is costly for equity holders to verify or prove any managerial wrongdoing for a third party such as a court. Management chooses the distribution of equity ownership so as to maximize private benefits against the risk of potential control challenges. When shareholders are long term oriented, then outside shares trade at a premium over their value to management, and management is inclined to sell of its equity stake to dispersed outsiders. When shareholders are short-term oriented, then outside share trade at a discount below their value to management, and disciplinary pressure can be substantially reduced via strategic share purchases.

This article shows that introducing derivative assets increases incentives to collect information about asset payoffs. The increase in information collection makes the price of the underlying asset more informative and causes the expected price to increase. Extending the model to a dynamic setting with multiple risky assets, we find the introducing derivative assets for one asset increases the expected prices of positively correlated assets and reduces price reaction to future earnings announcements. These findings are consistent with the bulk of the empirical evidence on the relationship between the introduction of derivative assets and the behavior of asset prices.