Dear all,

I am currently working on a panel data with a dataset from 1999, 2008 and 2017

In my linear regression model I have included independent variables from all three time periods, and two independent variables that are only included in the 2008 and 2017 dataset. When these two variables are included in the regression model, it leads to the regression model excluding all data from the 1999 dataset.

Is there a way to include the two independent variables which are only included in the 2008 and 2017 dataset in a regression model, while still getting to use the data from 1999 in the same regression model?

Thank you