在研究信贷融资歧视问题,变量中有表示产权性质的虚拟变量state,用xtreg,fe 的话,state会被omitted,控制行业的话,行业没有被omitted。请问这是怎么回事?是产权性质与其他变量共线了吗?我参考的论文上面也是用这些变量,没有被omitted的呀。用xtscc,state也会被omitted;用xtgls,state不会被omitted。
Fixed-effects (within) regression Number of obs = 4,122
Group variable: code Number of groups = 941
R-sq: Obs per group:
within = 0.1828 min = 1
between = 0.0360 avg = 4.4
overall = 0.0397 max = 8
F(7,3174) = 101.41
corr(u_i, Xb) = -0.3672 Prob > F = 0.0000
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interest7_w | Coef. Std. Err. t P>|t| [95% Conf. Interval]
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size_w | .693881 .0316888 21.90 0.000 .6317484 .7560137
growth_w | -.0479629 .064447 -0.74 0.457 -.1743248 .078399
roa_w | .9044015 .5748838 1.57 0.116 -.2227799 2.031583
lev_w | -2.540417 .18585 -13.67 0.000 -2.904815 -2.176018
tangible_w | .0560173 .0463844 1.21 0.227 -.0349291 .1469637
ipm_w | -.0016318 .0007819 -2.09 0.037 -.0031649 -.0000987
cash_wzj_w | .5827757 .1094782 5.32 0.000 .3681205 .7974309
state | 0 (omitted)
_cons | -16.70954 .7016665 -23.81 0.000 -18.0853 -15.33377
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sigma_u | 1.3099491
sigma_e | .58583211
rho | .83333094 (fraction of variance due to u_i)
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F test that all u_i=0: F(940, 3174) = 13.77 Prob > F = 0.0000