NO.PZ201512300100000301
问题如下：
1. The inclusion of index returns prior to 2001 would be expected to:
选项：
A.bias the historical equity risk premium estimate upwards.
B.bias the historical equity risk premium estimate downwards.
C.have no effect on the historical equity risk premium estimate.
解释：
A is correct.
The backfilling of index returns using companies that have survived to the index construction date is expected to introduce a positive survivorship bias into returns.
老师这道题不理解，用2001年之前的数据去测试，在这之前市场比较平稳，那相对来说Rm不是偏低嘛，那Rm-Rf的市场risk premium也是小的
现在2004-2006有动荡，所以Rm变大，risk premium也大，
所以如果用2001的数据的话不是risk premium有down bias吗
