Hi folks,

I run a fixed effect logit model. I am interested in capturing the nonlinear effect of a quadratic term. So a sample code will look like the following:

Code:
 xtlogit DV c.IV##c.IV controls, fe
The IV has a minimum of 1 and a maximum of 40, and mean of 8. Then, I want to obtain compute the margins so that I can plot the graph. The code is as follows:

Code:
margins, at(IV=(1(1)40))
marginsplot
However, I obtained the following suggesting that the parameters are not estimable.

Code:
------------------------------------------------------------------------------
             |            Delta-method
             |     Margin   Std. Err.      z    P>|z|     [95% Conf. Interval]
-------------+----------------------------------------------------------------
         _at |
          1  |          .  (not estimable)
          2  |          .  (not estimable)
          3  |          .  (not estimable)
          4  |          .  (not estimable)
          5  |          .  (not estimable)
          6  |          .  (not estimable)
          7  |          .  (not estimable)
          8  |          .  (not estimable)
          9  |          .  (not estimable)
         10  |          .  (not estimable)
         11  |          .  (not estimable)
         12  |          .  (not estimable)
         13  |          .  (not estimable)
         14  |          .  (not estimable)
         15  |          .  (not estimable)
         16  |          .  (not estimable)
         17  |          .  (not estimable)
         18  |          .  (not estimable)
         19  |          .  (not estimable)
         20  |          .  (not estimable)
         21  |          .  (not estimable)
         22  |          .  (not estimable)
         23  |          .  (not estimable)
         24  |          .  (not estimable)
         25  |          .  (not estimable)
         26  |          .  (not estimable)
         27  |          .  (not estimable)
         28  |          .  (not estimable)
         29  |          .  (not estimable)
         30  |          .  (not estimable)
         31  |          .  (not estimable)
         32  |          .  (not estimable)
         33  |          .  (not estimable)
         34  |          .  (not estimable)
         35  |          .  (not estimable)
         36  |          .  (not estimable)
         37  |          .  (not estimable)
         38  |          .  (not estimable)
         39  |          .  (not estimable)
         40  |          .  (not estimable)
------------------------------------------------------------------------------
I was wondering if anyone knows what is wrong here?

Thanks.