HOW LARGE ARE LEARNING EXTERNALITIES? *

The quantitative features of human capital externalities are not fully understood. Although static externalities are estimated in some studies, learning externalities remain mostly unestimated. By calibrating a growth model, this article provides an estimate of learning externalities. The calibration uses an equilibrium condition that equates private returns on physical capital and human capital. The results suggest that sizable learning externalities exist, even in a conservative setup. The estimated social rate of return on human capital is 9.0%, compared to the private rate of return, 6.6%. Therefore, human capital externalities are an important source of economic growth.