We examine the form, adoption rates, and economic rationale for various mutual fund investment restrictions. A sample of U.S. domestic equity funds from 1994 to 2000 reveals systematic patterns in investment constraints, consistent with an optimal contracting equilibrium in the fund industry. Restrictions are more common when (i) boards contain a higher proportion of inside directors, (ii) the portfolio manager is more experienced, (iii) the fund is managed by a team rather than an individual, and (iv) the fund does not belong to a large organizational complex. Low- and high-constraint funds produce similar risk-adjusted returns, also consistent with an optimal contracting equilibrium.

Aït‐Sahalia (1996) and Stanton (1997) use nonparametric estimators applied to short‐term interest rate data to conclude that the drift function contains important nonlinearities. We study the finite‐sample properties of their estimators by applying them to simulated sample paths of a square‐root diffusion. Although the drift function is linear, both estimators suggest nonlinearities of the type and magnitude reported in Aït‐Sahalia (1996) and Stanton (1997) . Combined with the results of a weighted least squares estimator, this evidence implies that nonlinearity of the short rate drift is not a robust stylized fact.

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.