Dear all,

I currently am stuck with a theoretical question, and was wondering whether any of you may know the answer to this. It is a general question, for which I give an example as illustration. Say I have data for the years 1990 until 2010 for 20 countries. I do the regression y=a+bx+e where a is a constant and b is the coefficient for the independent variable and e the error term. In this this panel setting, I run an OLS regression first without and then with interaction terms (x variable interacted with decade dummies). Is it possible that in the former case the b-coefficient is statistically significant (at e.g. the 5% level), but when I interact it with the decade dummies (1990,2000,2010) and then run the -margins- command, I fail to find a statistically significant coefficient b at the 5% level for any of the three decades?

I guess what I would like to know is if evidence of a significant coefficient over the complete period considered, guarantees that it would be present in at least one of the individual decades?

This is more of a curiosity/theoretical question, where I am trying to improve my understanding of interaction terms coefficients interpretation and the -margins- command results. Any help on this nevertheless would be greatly appreciated.

Best,

Satya