“…Research on returns to college education has carefully and often ingeniously addressed whether this result holds in the presence of various challenges to the exogenous selection assumption (also known as the no-confounding assumption). These studies used various research designs to mitigate the effect of non-random selection on unobservable factors, such as individual-level innate ability, including in twin studies and sibling fixed effects (Angrist and Krueger, 1991;Ashenfelter and Krueger, 1994;Altonji and Dunn, 1996;Behrman et al, 1996;Ashenfelter and Rouse, 1998;Rouse, 1999;Duflo, 2001;Heckman and Vytlacil, 2001;Estrada and Gignoux, 2017). If a sufficiently large number of people enroll in the same graduate program, thereby increasing the supply of suitable candidates within this particular skill group, then the competition for jobs will increase, resulting in a lower price of labor within the skill group; consequently, employment rates and earnings will drop.…”