Omitted "Treatment" variable in DiD fixed panel regression

[Jiin Lee]

Hi, I'm currently studying the effects of mandatory CSR disclosure on firm performance. My data set consists of firm-year variables from 27 EU countries from 2011 to 2018. I generate variable "Post" if the year is greater than 2014.
My treatment group is firms in countries with non-compliance penalties. It is actually based on country, not firm. So, my regression command is as follows:

xtreg ROA_NI_w post treatment post_treat size cash fd gr i.SICcode i.year, fe

(I didn't add i.country since "treatment" is based on the country. If this is wrong, please let me know.)

and I got results as below:

Fixed-effects (within) regression Number of obs = 8,285
Group variable: compid Number of groups = 1,187

R-sq: Obs per group:
within = 0.0374 min = 2
between = 0.1029 avg = 7.0
overall = 0.0460 max = 7

F(11,7087) = 25.04
corr(u_i, Xb) = 0.1048 Prob > F = 0.0000

------------------------------------------------------------------------------
ROA_NI_w | Coef. Std. Err. t P>|t| [95% Conf. Interval]
-------------+----------------------------------------------------------------
post | .27638 .4879204 0.57 0.571 -.6800898 1.23285
treatment | 0 (omitted)
post_treat | -.4764226 .4547777 -1.05 0.295 -1.367923 .4150775
size | 4.360291 .3508205 12.43 0.000 3.672578 5.048004
cash | 9.076161 1.061664 8.55 0.000 6.994982 11.15734
fd | .8019895 3.059513 0.26 0.793 -5.195571 6.79955
gr | 19.24324 4.655786 4.13 0.000 10.11651 28.36997
(For the rest of results, they are omitted to save the space.)

I don't know why "treatment" is omitted. When I included i.country, the "treatment"" omitted as well. I don't know what should I do for solving this issue?
I attach pictures of my dataset. Thank you in advance.

[William Lisowski]

Welcome to Statalist.

My guess is that your firms are nested within countries, so that treatment which is based on country is constant within each firm, and by using a fixed effects regression (the fe option on your xtreg command) you are including firm fixed effects, and thus the treatment effect is totally determined by the country within which the firm exists.

With that said, some advice if you have further questions on this topic.

You have accidentally posted your topic in Statalist's Mata Forum, which is used for discussions of Stata's Mata language, which is different than Stata's command language, and different than Stata's matrix commands. Your question will see a more appropriate, and much larger audience if you post it in Statalist's General Forum.

Also, if you have not already done so, take a look at the Statalist FAQ linked to at the top of this page for posting guidelines and suggestions.

[Jiin Lee]

Thank you very much for letting me know and thank you for your answer as well!
I will post it in General Forum!