Specifying human capital

A review of the measures of the stock of human capital used in empirical growth research - including adult literacy rates, school enrollment ratios, and average years of schooling of the working-age population - reveals that human capital is mostly poorly proxied. The simple use of the most common proxy, average years of schooling, misspecifies the relationship between education and the stock of human capital. Based on human capital theory, the specification of human capital is extended to allow for decreasing returns to education and for differences in the quality of a year of education. The different specifications give rise to hugely differing measures of the stock of human capital across countries, and development-accounting results show that misspecified human capital measures can lead to severe underestimation of the development effect of human capital.