Estimating Marginal Returns to Education
Pedro Carneiro, James Heckman, Edward Vytlacil
American Economic Review, vol. 101, 2011, p. 2754-2781.

Evaluating Marginal Policy Changes and the Average Effect of Treatment for Individuals at the Margin
Pedro Carneiro, James Heckman, Edward Vytlacil
Econometrica, vol. 78, 2010, p. 377-394.