为什么BR可以直接等同于选股数量？

问题如下：

Based on the fundamental law of active management, if a portfolio manager has an information ratio of 0.75, an information coefficient of 0.1819, and a transfer coefficient of 1.0, how many securities are in the portfolio manager’s fund, making the assumption that the active returns are uncorrelated.

选项：

About 2

About 4

About 17

解释：

C is correct.

Using the equation $IR\ast=IC\times\sqrt{BR}$ and assuming that breadth can be interpreted as number of securities in the portfolio, solving for breadth in the equation above yields ${(\frac{0.75}{0.1819})}^2$ = 17.000.

考点：the full fundamental law

解析：根据$IR=TC\times IC\times\sqrt{BR}$，IR=0.75，IC=0.1819，TC=1，因此BR=17。