st: some problems with xtreg that I cannot explain

[Narasimhan Sowmyanarayanan <narasimhan.sowmyanarayanan@gmail.com>]

Hi All:

I am running xtreg command with fixed effects.

In one of the models I find the following output -- note that the F value is

The syntax is a simple

xtreg Y X1 X2 (a vector of X's), fe robust

********************************************
Fixed-effects (within) regression               Number of obs      =      2459
Group variable: gvkey                           Number of groups   =       464

R-sq:  within  = 0.0944                         Obs per group: min =         1
       between = 0.0824                                        avg =       5.3
       overall = 0.0798                                        max =        24

                                                F(43,463)          =     80.50
corr(u_i, Xb)  = -0.0357                        Prob > F           =    0.0000

****************************************************

A slightly different regression with a linear and square term (not
included above) gives me the below mentioned results. The model
converges but does not give me any F value and shows a "dot" in that
space? I would highly appreciate any insights on this.

*******************************************************************************
Fixed-effects (within) regression               Number of obs      =      2459
Group variable: gvkey                           Number of groups   =       464

R-sq:  within  = 0.1574                         Obs per group: min =         1
       between = 0.1333                                        avg =       5.3
       overall = 0.1414                                        max =        24

                                                F(44,463)          =         .
corr(u_i, Xb)  = -0.0514                        Prob > F           =         .
**************************************************************************************

Thanks
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