Short Rate Dynamics and Regime Shifts-super-

We characterize the dynamics of the US short-term interest rate using a Markov regime-switching model. Using a test developed by Garcia, we show that there are two regimes in the data: In one regime, the short rate behaves like a random walk with low volatility; in another regime, it exhibits strong mean reversion and high volatility. In our model, the sensitivity of interest rate volatility to the level of interest rate is much lower than what is commonly found in the literature. We also show that the findings of nonlinear drift in Aït-Sahalia and Stanton, using nonparametric methods, are consistent with our regime-switching model. Copyright (c) 2009 The Authors. Journal compilation (c) International Review of Finance Ltd. 2009.