1. Ainslie, R. C. (1985). The psychology of twinship. Lincoln, NE: University of Nebraska Press.
2. Does compulsory school attendance affect schooling and earnings?;Angrist;Quarterly Journal of Economics,1991
3. Estimates of the economic return to schooling from a new sample of twins;Ashenfelter;American Economic Review,1994
4. Income, schooling, and ability: Evidence from a new sample of identical twins;Ashenfelter;Quarterly Journal of Economics,1998
5. Growth and development of twins of dissimilar size at birth;Babson;Pediatrics,1964