With only one observation per country, it is impossible to control for unobserved heterogeneity across countries.

由于每个国家只有一个观测结果，因此不可能控制各国间未观察到的异质性。

youdao

With only one observation per country, it is impossible to control for unobserved heterogeneity across countries.

由于每个国家只有一个观测结果，因此不可能控制各国间未观察到的异质性。

youdao