The Difference Between an Unbalanced and a Balanced Panel Is

Multiple Choice

The difference between an unbalanced and a balanced panel is that

A) you cannot have both fixed time effects and fixed entity effects regressions.
B) an unbalanced panel contains missing observations for at least one time period or one entity.
C) the impact of different regressors are roughly the same for balanced but not for unbalanced panels.
D) in the former you may not include drivers who have been drinking in the fatality rate/beer tax study.