一个有效的工具变量应满足如下两个条件
A.corr(Zi, Xi) = 0 and corr(Zi, ui) ≠ 0
B.corr(Zi, Xi) = 0 and corr(Zi, ui) = 0.
C.corr(Zi, Xi) ≠ 0 and corr(Zi, ui) = 0
D.corr(Zi, Xi) ≠ 0 and corr(Zi, ui) ≠ 0
- · 有4位网友选择 A,占比44.44%
- · 有3位网友选择 B,占比33.33%
- · 有2位网友选择 C,占比22.22%
A.corr(Zi, Xi) = 0 and corr(Zi, ui) ≠ 0
B.corr(Zi, Xi) = 0 and corr(Zi, ui) = 0.
C.corr(Zi, Xi) ≠ 0 and corr(Zi, ui) = 0
D.corr(Zi, Xi) ≠ 0 and corr(Zi, ui) ≠ 0
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