Due to a tax law implemented in 1998, Dutch employers can claim an extra tax deduction when they train employees aged 40 years or older. This causes a discontinuity in a firm's cost of training an employee. We exploit this discontinuity to identify two effects: the effect of the tax deduction on...

I show that in a conventional Ramsey model, between one-fourth and one-half of the global income distribution can be explained by a single factor: The effect of large, persistent differences in national average IQ on the private marginal product of labor. Thus, differences in national average IQ...

Human capital plays an important role in the theory of economic growth, but it has been difficult to measure this abstract concept. We survey the psychological literature on cross-cultural IQ tests, and conclude that modern intelligence tests are well-suited for measuring an important form of a...

This paper reports about a randomized field experiment in which first year economics and business students at the University of Amsterdam could earn financial rewards for passing the first year requirements within one year. Participants were assigned to a high, low and zero (control) reward...

I show that in a conventional Ramsey model, between one-fourth and one- half of income differences across countries can be explained by a single factor: The steady-state effect of large, persistent differences in national average IQ on worker productivity. These differences in cognitive...

This study estimates the effect of expanding enrollment possibilities in early eduction on the achievement of young children. To do so it exploits two features of the Dutch schooling system. First, children are allowed to enroll in school on their fourth birthday. Second, children having their...