命令是： xtgls lgdp limport lfdi lk natu,t(year) panels(corre)

估计结果是：

Cross-sectional time-series FGLS regression

Coefficients:  generalized least squares
Panels:        heteroskedastic with cross-sectional correlation
Correlation:   no autocorrelation

Estimated covariances      =       435           Number of obs      =       377
Estimated autocorrelations =         0            Number of groups   =        29
Estimated coefficients     =            5             ime periods       =        13
Wald chi2(4)       =  48935.93
Log likelihood             =         .                     Prob > chi2        =    0.0000

回归系数略；

Note: you estimated at least as many quantities as you have observations.

请教：log likelihood值为什么会缺失呢？还有回归结果下的Note说明了什么呢？回归数据是平行面板．谢谢！！！