Random-effects GLS regression Number of obs = 28091
Group variable: idcode Number of groups = 4697
R-sq: within = 0.1715 Obs per group: min = 1
between = 0.4759 avg = 6.0
overall = 0.3671 max = 15
Wald chi2(9) = 9189.95
corr(u_i, X) = 0 (assumed) Prob > chi2 = 0.0000
ln_wage Coef. Std. Err. z P>z [95% Conf. Interval]
grade .0661586 .0017637 37.51 0.000 .0627018 .0696155
age .0363061 .0031193 11.64 0.000 .0301925 .0424198
age2 -.000705 .00005 -14.10 0.000 -.0008029 -.000607
ttl_exp .0292322 .0024237 12.06 0.000 .0244818 .0339826
exp2 .0002946 .0001163 2.53 0.011 .0000666 .0005225
tenure .0390982 .0017557 22.27 0.000 .035657 .0425393
tenure2 -.0020014 .0001193 -16.77 0.000 -.0022353 -.0017676
not_smsa -.1268951 .0071494 -17.75 0.000 -.1409076 -.1128825
south -.0947153 .0071622 -13.22 0.000 -.108753 -.0806775
_cons .2135133 .0492919 4.33 0.000 .1169029 .3101237
sigma_u .25896298
sigma_e .29068923
rho .44247107 (fraction of variance due to u_i)
请问Wald chi2(9) = 9189.95
corr(u_i, X) = 0 (assumed) Prob > chi2 = 0.0000这个代表什么意思,有什么实际意义。