To check balance explicitly:
Not including year dummies can make your FE model pick up economy-wide trends and claim them as treatment effects. Solution: Always include i.year or use xtreg, fe with time dummies. stata panel data
Allows for arbitrary correlation within entities. To check balance explicitly: Not including year dummies
Fixed Effects (preferred due to ability bias) xtreg wage union experience i.year, fe robust stata panel data
Visualization:
Success in Stata panel data analysis is 80% data preparation.