方差为什么不用带百分号

问题如下：

let’s consider the performance of the Russell 1000 between February 1990 and December 2016. The monthly arithmetic return was 0.878%, and the volatility, as measured by the standard deviation of return, was 4.199%. What is the geometric return?

选项：

A.

0.79%

B.

0.62%

C.

0.54%

解释：

We know that the expected compounded/geometric return of an asset (Rg) is approximately related to its expected arithmetic/periodic return (Ra) and its expected volatility (σ):

$R_g=R_a-\frac{\sigma^2}2$

$R_g=0.878\%-\frac{4.199\%^2}2=0.79\%$