Equalization or Selection? Reassessing the Meritocratic Power of a College Degree in Intergenerational Income Mobility

higher education's impact on mobility is driven by selection effects,

"....estimate the degree of intergenerational income mobility among college graduates purged of selection processes that may drive up observed mobility in this subpopulation. Analyzing data from the National Longitudinal Survey of Youth 1979,I find that once selection processes are adjusted for, intergenerational income mobility among college graduates is very close to that among non-graduates.This finding suggests that expanding the pool of college graduates per se is unlikely to boost intergenerational income mobility in the United States..... In fact, to the extent that college graduates from low and moderate-income families are more selected on such individual attributes as ability and motivation than those from high-income families, the high mobility observed among bachelor’s degree holders may simply reflect varying degrees of selectivity of college graduates from different family backgrounds. This study represents my attempt to distinguish the equalization and selection effects of college. First, I formalized the selection process using the language of DAGs, and defined two measures of intergenerational mobility—conditional mobility and controlled mobility—for college graduates. While conditional mobility reflects what we observe among actual college graduates, controlled mobility reflects what we would observe if, given parental income, college graduation did not depend on other predictors of adult family income. By fixing the associations between parental income and a range of pre-college individual characteristics at their baseline levels in the general population, controlled mobility disentangles the causal effect of college from selection processes, thus directly informing the degree to which we can promote mobility by expanding the pool of college graduates. Then, I employed a novel reweighting method, called “residual balancing,” to estimate controlled mobility empirically. Using the NLSY79 data, I examined the equalization effects of both college completion in general and selective/nonselective colleges in particular. Results show that while conditional mobility is substantially higher among college graduates than non-graduates, controlled mobility differs little between the two groups. When we break down college graduates into those who attended selective institutions and those who did not, we find little evidence for an equalizing effect of nonselective colleges. Selective colleges, on the other hand, exhibit a substantively large, yet statistically insignificant, equalizing effect.Overall, our findings suggest that the “college premium” in intergenerational income mobility is largely driven by selection processes rather than an equalizing effect of a baccalaureate degree.....As shown in Figure 3, family income correlates strongly not only with other ascribed characteristics such as race, ethnicity, mother’s education, and family structure, but also with achieved characteristics such as cognitive ability and educational expectations. It is the combination of these origin-based differences that perpetuate and reproduce inequality—by shaping the type of postsecondary institutions attended, the degree of engagement in the college extracurriculum, the level of parental economic support after graduation, and patterns of marital formation and partner choice. As a result, the overall influence of parental income stays unabated among college graduates, despite the appearance of high (conditional) mobility in this subpopulation...."
Xiang Zhou, "Equalization or Selection? Reassessing the “Meritocratic Power” of a College Degree in Intergenerational Income Mobility,"American Sociological Review, April 30, 2019, https://journals.sagepub.com/doi/abs/10.1177/0003122419844992