问一道题：NO.PZ2017092702000050

问题如下：

For 2009–2013, the mean absolute deviation of the MSCI World Index total returns is closest to:

选项：

10.20%.

12.74%.

16.40%

解释：

A is correct.

The formula for mean absolute deviation (MAD) is $MAD=\frac{\displaystyle\sum_{i=1}^n{\vert X_i-\overline X\vert}}n$   Column 1: Sum annual returns and divide by n to find the arithmetic mean ( $\overline X$ ) of 16.40%. Column 2: Calculate the absolute value of the difference between each year’s return and the mean from Column 1. Sum the results and divide by n to find the MAD. These calculations are shown in the following table: