In statistics and econometrics, the first-difference (FD) estimator is an estimator used to address the problem of omitted variables with panel data. It is consistent under the assumptions of the fixed effects model. In certain situations it can be more efficient than the standard fixed effects (or "within") estimator.
First differences are the differences between consecutive y-‐values in tables of values with evenly spaced x-‐values. If the first differences of a relation are constant, the relation is _______________________________ If the first differences of a relation are not constant, the relation is ___________________________
