Hi all,

I am estimating the following model using fixed effects including linear time trends.

Code:
xtreg lemp lunion lunemployment lfertility lyouth i.year i.id##c.year, fe vce(cluster id)
Due to concerns the fertility may be endogenous, I am also using 2SLS, and the following code.

Code:
xtivreg lemp lunion lunemployment lyouth i.year (lfertility = lagfertility), fe vce(cluster id)

When I try to include the linear time trend i.id##c.year the following message is displayed:

Code:
independent variables are collinear with the panel variable id
My question is, is it possible to include linear time trends with instrumental variable estimation?