Hello!
I am a new user of Stata software.
I am writting my final essay on the effect of union density on unemployment rate in OECD countries. My control variables are education, GDP and unemployment benefit. I am using panel data from 1990-2017 on 34countries, and they are divided into four groups according to their bargaining systems (group 1, group2, group3, and group 4).
My questions are:
1) for year and country dummies , will I add them all in my model? because they are 28 dummies yr_1...............y_28

2) If i create interaction of group dummies with measure of unionization , as example interaction 1= group1*uniondensity, will I add this interaction1 variable in my regression and also include union density? or i can only have interaction1 in the regression without union density in the model? or i can interact in another way?

I appreciate your advices