* setup xtset id year
By using the fe suffix, Aris was essentially telling Stata to ignore the differences between countries and focus only on what happened within them over time. It was a surgical strike against omitted variable bias. The "fixed" part of the model absorbed the unique, unchanging personality of each nation, leaving only the pure relationship between price and supply. The Great Debate: Hausman’s Shadow stata panel data exclusive
xtabond y L.y x1 x2