Robert Litterman and Jose Scheinkman were the first to study how changes in the shapes of the yield curve affect the total return on the Treasury securities. The historical returns can be explained using three factors: the changes in the level of rates, changes in the slope of the yield curve, and the changes in the curvature of the yield curve. The first factor is the largest contributing factor for the change in treasury returns. Therefore, the managers of treasury portfolios should control the exposure to changes in the level of interest rates. Duration measure can be used to quantify such risks. The second factor is the next largest contributor to the change in returns. However, the second factor is only 1/10 as significant as the first factor. The third factor contributes very little to the changes in returns.