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扑扑扑 · 2020年08月01日

问一道题:NO.PZ2017092702000132

问题如下:

An analyst tests the profitability of a trading strategy with the null hypothesis being that the average abnormal return before trading costs equals zero. The calculated t-statistic is 2.802, with critical values of ± 2.756 at significance level α = 0.01. After considering trading costs, the strategy’s return is near zero. The results are most likely:

选项:

A.

statistically but not economically significant.

B.

economically but not statistically significant.

C.

neither statistically nor economically significant.

解释:

A is correct.

The hypothesis is a two-tailed formulation. The t-statistic of 2.802 falls outside the critical rejection points of less than –2.756 and greater than 2.756, therefore the null hypothesis is rejected; the result is statistically significant. However, despite the statistical results, trying to profit on the strategy is not likely to be economically meaningful because the return is near zero after transaction costs

这道题我们所相信的(备择假设)是超额收益不等于0. 但这个设想本身就是在“before trading cost”的前提下的呀。后来实际验证时候,考虑到了trading cost,return才接近0(意味着如果跟最初设想时候的前提一致,即before trading cost,收益的确≠0).所以应当是经济学上有意义的呀?

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已采纳答案

星星_品职助教 · 2020年08月01日

同学你好,

这里面有两个概念,角度不同。

首先是统计上的检验,这种情况不考虑trading cost,所以得出结论是return显著不为0,所以从纯统计的角度,我们应该采用这种策略。也就是statistically significant。

 其次是经济学意义上的检验,由于经济学是考虑实务中的trading cost的,所以实际验证后,统计上有显著回报的策略在实务中回报率变成0了,所以这种方式在经济学角度是没有意义的。也就是not economically significant。

“before trading cost”的前提下考虑的就是统计学上的检验,这种情况只是统计学上有意义。但不是经济学上有意义。

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