1. The World Bank https://www.vsemirnyjbank.org/ru/publication/human-capital/brief/the-human-capital-project-frequently-asked-questions
2. Schultz T.W, Education and economic growth. In Social Forces Influencing American Education (University of Chicago Press, Chicago, IL, USA, 1961), pp. 85-90
3. Becker G.S., Human Capital: A Theoretical and Empirical Analysis, with Special Reference to Education (Columbia University Press, New York, NY, USA, 1964)
4. Increasing Returns and Long-Run Growth