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yukijiang · 2019年09月24日

问一道题:NO.PZ2017092702000132 [ CFA I ]

问题如下图:

选项:

A.

B.

C.

解释:

statistic上和economic上的前提(一个是扣除cost之前,一个是扣除cost以后)都不一样啊,得出来结果不一致,很正常吧?前提不一致,算出来的结果怎么能互相对比呢?如果两个前提假设都是扣除成本以后的数值,结果是不是会一致了?

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星星_品职助教 · 2019年09月24日

同学你好,

这道题和这个考点并不是考察用两种方式都去做检验然后对比结果的。而是想说明:在统计学意义上的显著(不为0),可能不一定在经济学上显著。即从统计学角度来看有意义的事,可能却没有实际经济意义。

具体而言,这道题通过统计学做假设检验的方式说明了这个策略的平均超额收益不为0,所以这个策略从统计学角度上来讲是可以用的,能赚到超额收益(average abnormal return的意思即为平均来看,这个策略能给投资者带来超额收益)。

但是如果从实际经济学意义的角度来看,一个策略不能只看本身是否能赚到钱,而是还要扣除交易成本和税费。但扣完了这些后平均超额收益就几乎是0了,所以这个策略从经济学的角度来看是没有意义的。

所以这就是统计学角度不扣除成本,但经济学角度扣成本的原因。

这个不是一个重点考点,其实想说明的就是:有时候从统计学上看这件事可以做,但是在实际中真做了的话却可能却没有(经济学意义上的)好处,理解到这个程度就可以了,加油

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