Income, Schooling, and Ability: Evidence from a New Sample of Identical Twins
利用约700对同卵双胞胎数据，估计教育回报率平均为9%，发现能力较低者回报略高，且能力高者因教育边际成本低而非收益高而多受教育。
We develop a model of optimal schooling investments and estimate it using new data on approximately 700 identical twins. We estimate an average return to schooling of 9 percent for identical twins, but estimated returns appear to be slightly higher for less able individuals. Simple cross-section estimates are marginally upward biased. These empirical results imply that abler individuals attain more schooling because they face lower marginal costs of schooling, not because of higher marginal benefits.