3. Ashenfelter, O., & Krueger, A. (1994). Estimates of the Economic Return to Schooling from a New Sample of Twins. American Economic Review, 84, 1157-1174. [OpenAIRE]
4. Autor, & Katz. (1999). Changes in the Wage Structure and Earnings Inequality. От O. A. (Eds.), Handbook of Labour Economics, Volume 3, Chapter 25 (стр. 1463-1555). New York: North-Holland.
5. Becker, G. S. (1964). Human Capital: A Theoretical and Empirical Analysis, with Special Reference to Education. NBER, Columbia University Press.
6. Becker, G. S. (1994). Human Capital: A Theoretical and Empirical Analysis with Special Reference to Education (3rd Edition). National Bureau of Economic Research, Inc.
7. Becker, G. S., & Chiswick, B. R. (1966). Education and the Distribution of Earnings. The American Economic Review, Vol. 56, No. 1/2 (Mar. 1, 1966), pp. 358-369.
8. Becker, G., Murphy, K., & Tamura, R. (1990). Human Capital, Fertility, and Economic Growth. Journal of Political Economy, Vol. 98, No. 5, part II, S12-S37.
9. Ben-Porath, Y. (1967). The Production of Human Capital and the Life Cycle of Earnings. The Journal of Political Economy, Vol. 76, No. 4, PArt 1 (Aug.,1967), 352- 365. [OpenAIRE]
10. Bingley, P., Christensen, K., & Walker, I. (2009). The Returns to Observed and Unobserved Skills Over Time: Evidence from the Panel of Population of Danish Twins. Danish National Institute for Social Research.
11. Blau, F. D., & Kahn, L. M. (1996). International Differences in Male Wage Inequality: Institutions versus Market Forces. NBER Working Papers 4678, National Bureau of Economic Research, Inc.
12. Booth, A., & Satchell, S. (1995). The Hazards of Doing a PhD: An Analysis of Completion and Withdrawal Rates of Birtish PhD Students in the 1980s. Journal of The Royal Statistical Society. Series A (Statistics in Society), Vol. 158, No. 2, 297-318. [OpenAIRE]
13. Brand, J. E., & Xie, Y. (2010). Who Benefits Most from College?: Evidence for Negative Selection in Heterogeneous Economic Returns to Higher Education. American Sociological Review, nº75, vol.II, 273-302.
14. Buchinsky, M. (2001). Quantile regression with sample selection: Estimating women's return to education in the U.S. Empirical Economics, 26, issue 1, 87-113. [OpenAIRE]
15. Cameron, C., & Trivedi, P. K. (2005). MICROECONOMETRICS: Methods and Applications. New York: Cambridge University Press.
16. Card, D. (1999). The Causal Effect of Education on Earnings. От O. A. Card, Handbook of Labour Economics, Volume 5 (стр. 1801-1863). New York: North-Holland.
17. Card, D., & Krueger, A. (1992). Does School Quality Matter? Returns to Education and Characteristics of Public Schools in the United States. Journal of Political Economy, Vol. 100, No. 1 (Feb.,1992), pp. 1-40.