suppose that we use the historical geometric mean for U.S. equity of 4.8 percent to value Citibank Inc. (NYSE: C) as of early January 2006. According to Standard & Poor’s, Citibank had a beta of 1.32 at that time. Using the 10-year U.S. Treasury bond yield of 4.38 percent to represent the risk-free rate, the estimate of the cost of equity for Citibank is 4.38 percent+1.32(4.8 percent)= 10.72 percent.
为什么不是4.38+1.32（4.8-4.32）？呢