M any models of yield curve shape have been proposed: from stochastic, to fundamental, to principal components. Most models are concerned with either achieving goodness of fit, given "rationality criteria"; the ability to forecast the level or slope of the term structure; or the ability to generate scenarios for pricing and immunization applications. With the exception of work on convexity bias, there is little work on predicting the curvature of the yield curve beyond eighteen months.Investment managers are keenly interested in models of the yield curve into which expectations can be embedded so that the analysis can be used to direct investments. To provide a model of yield curve shape that is effective for investment management, we must answer four questions: 1) which yield curve model should be used; 2) what a priori assumptions should be made; 3) how should the shape parameters be forecast; and 4) how effective are the forecasts for investment purposes.We summarize some of the major threads in term structure modeling as they pertain to the curvature of the term structure. We discuss why shape is important for investment management and evaluate a simple forecasting mechanism for the shape parameter.
I. TYPES OF YIELD CURVE MODELS AND THEIR PREDICTIVE STRENGTHSYield curve models can be classified into three types:1. Stochastic, arbitrage-free. 2. Principal components. 3. Fundamental.The stochastic arbitrage-free models, such as Brennan and Schwartz [1982] and Heath, Jarrow, and Morton [1990], develop interest rate processes, given an underlying random variable (or variables), that: 1) meet rationality criteria, or 2) are unlikely to generate yield curves with arbitrage opportunities. One survey of such approaches, Chan et al. [1992], highlights their emphasis on the relationship between level of interest rates and volatility assumption for the random variable.Boero and Torricelli [1996] point out that many of the theories explain the term structure, given the long and short rates, especially Brennan and Schwartz. Boero and Torricelli also assert that Ho-Lee [1986] and the Heath, Jarrow, and Morton [1990] models are not models of the term structure, only models of how to price contingent claims.Because these models are designed for use in options pricing, the mean does not play a role. The mean, however, is very important to investment managers because it is the primary measure affecting a manager's view. We do not use stochastic models to predict any component of the yield curve shape.Principal components analysis (PCA) focuses on finding orthogonal factors, in the space of actual interest rate changes, that