Generally Speaking, What Are the Methods Available to the Econometrician

Multiple Choice

Generally speaking, what are the methods available to the econometrician who wants to estimate a linear model with a fixed effects model design (i.e., dummy variable for individual units observed over multiple periods) ?

A) Within Estimator and Fixed Effects regression
B) Diff-in-diff and Two-stage least squares
C) Two-stage least squares and Fixed Effects regression
D) Within estimator and instrumental variable regression