basically, for a random selection, one should include firms with good performances and firms that performed badly. poeple argued that, the US sample may be problematic since it happens that all the US firms perform well. so this "special" sample can not tell the whole story, or it introduces some bias.

我也准备看啊！希望能多交流！

我在年初的时候看过，还写出了一个总结，希望大家交流。

这个文章应该很好 是一个综述性质的
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