You cannot estimate coefficients for variables that do not change over time (e.g., race or gender), as they are scrubbed out by the FE transformation. Random Effects (RE) Model
* Plot a single variable over time for all units (spaghetti plot) xtline gdp stata panel data
To see how many periods of data you have for each entity, use xttab : xttab industry Use code with caution. Line Plots You cannot estimate coefficients for variables that do