Esteban and Ray (Econometrica 1994) describe a measure of polarization that is closely connected to potential conflict or tension in a society, emphasizing the difference between polarization and inequality. In principle a very highly polarized society may have a low level of inequality...

Income gains from participation in economic programs are estimated as the difference between income with the program and that without it. The "with" data can be collected without much difficulty. But the "without" data are fundamentally unobserved, since an individual cannot be both a...