Fixed-effects (within) regression               Number of obs      =       348
Group variable: wave                            Number of groups   =        29

R-sq:  within  = 0.9633                         Obs per group: min =        12
       between = 0.9818                                        avg =      12.0
       overall = 0.9708                                        max =        12

                                                F(2,317)           =   4164.97
corr(u_i, Xb)  = -0.7074                        Prob > F           =    0.0000

------------------------------------------------------------------------------
      lngdp0 |      Coef.   Std. Err.      t    P>|t|     [95% Conf. Interval]
-------------+----------------------------------------------------------------
        lnk0 |   1.041084   .0147431    70.61   0.000     1.012077     1.07009
        lnl0 |   .2206183   .0337707     6.53   0.000     .1541753    .2870614
       _cons |  -3.632711   .3635147    -9.99   0.000    -4.347918   -2.917505
-------------+----------------------------------------------------------------
     sigma_u |  .22137242
     sigma_e |  .12545121
         rho |  .75691854   (fraction of variance due to u_i)
------------------------------------------------------------------------------
F test that all u_i=0:     F(28, 317) =    18.34             Prob > F = 0.0000

 里面的corr(u_i, Xb)  = -0.7074  是什么意思   说的是存在内生性吗？