Empirical studies of the modern theories of bond pricing typically choose proxies for the state variables in a rather arbitrary fashion. This paper empirically analyzes the question of the optimal spot rates to use as state variables. Our findings indicate that the four‐year spot rate serves as the best proxy in the one‐state‐variable model. In the case of the two‐state‐variables model, the six‐year rate and eight‐month rate are identified as best. Tests of the out‐of‐sample prediction ability indicate that our model is superior to Macaulay's duration model and alternative proxies for state variables.

S&P 500 index funds represent one of the simplest vehicles for examining rational behavior. They hold virtually the same securities, yet their returns differ by more than 2 percent per year. Although the relative returns of alternative S&P 500 funds are easily predictable, the relationship between cash flows and performance is weaker than rational behavior would lead us to expect. We show that selecting funds based on low expenses or high past returns outperforms the portfolio of index funds selected by investors. Our results exemplify the fact that, in a market where arbitrage is not possible, dominated products can prosper.