Typically, the yield curve depicts a line that rises from lower interest rates on shorter-term bonds to higher interest rates on longer-term bonds. Researchers in finance have studied the yield curve statistically and have found that shifts or changes in the shape of the yield curve are attributable to a few unobservable factors (Dai and Singleton 2000). Specifically, empirical studies reveal that more than 99% of the movement of various Treasury bond yields are captured by three factors, which are often called “level,” “slope,” and “curvature” (Litterman and Scheinkman 1991). The names describe how the yield curve shifts or changes shape in response to a shock, as shown in Figure 1. Panel A of Figure 1 illustrates the influence of a shock to the “level” factor on the yield curve. The solid line is the original yield curve, and the dashed line is the yield curve after the shock. A “level” shock changes the interest rates of all maturities by almost identical amounts, inducing a parallel shift that changes the level of the whole yield curve. Panel B shows the influence of the “slope” factor on yield curve. The shock to the “slope” factor increases short-term interest rates by much larger amounts than the long-term interest rates, so that the yield curve becomes less steep and its slope decreases. Panel C shows the response of the yield curve to a shock to the “curvature” factor. The main effects of the shock focus on medium-term interest rates, and consequently the yield curve becomes more “hump-shaped” than before.