I have a regression model and I have to investigate the effect in different cases (with/without time trend, fixed effects).
I want to run 6 different cases:
Time trend Corporate fixed effects Year fixed effects
Case 1 Yes No No
Case 2 No No No
Case 3 Yes Yes No
Case 4 Yes No Yes
Case 5 No Yes No
Case 6 No No Yes
I think that I have the following codes:
Case 1:
regress nettotoegevoegdewaarde schulden omzet arbeidsintensiteit aantalwerknemers BBPgroei loonkost

Case 3:
xtreg nettotoegevoegdewaarde schulden omzet arbeidsintensiteit aantalwerknemers BBPgroei loonkost, fe

Case 4:
xtreg nettotoegevoegdewaarde i.year schulden omzet arbeidsintensiteit aantalwerknemers BBPgroei loonkost

Are these codes correct?

Are these the 6 most important cases to investigate or should I add/delete something more?

The main question is: how can i Run a model without a time trend?

Thanks in advance.