Peer Effects in Higher Education

In this chapter, we describe the potential significance of student peer effects for the economic structure of and behavior in higher education. Their existence would motivate much of the restricted supply, student queuing, and selectivity and institutional competition via merit aid and honors colleges that we see in American higher education; their (appropriate) non-linearity could justify the resulting stratification of higher education as an efficient way to produce human capital. In addition, we use data from the College and Beyond entering class of 1989, combined with phonebook data identifying roommates, to implement a quasi-experimental empirical strategy aimed at measuring peer effects in academic outcomes. In particular, we use data on individual students' grades, SAT scores, and the SAT scores of their roommates at three schools to estimate the effect of roommates' academic characteristics on an individual's grades. The results suggest that, for two of the three schools used, students in the middle of the SAT distribution do somewhat worse in terms of grades if they share a room with a student who is in the bottom 15 percent of the SAT distribution. Students in the top of the SAT distribution appear often not to be affected by the SAT scores of their roommates. These results are similar to those reported in earlier research using data from Williams (Zimmerman) and Dartmouth (Sacerdote).

An Empirical Analysis of the Welfare Magnet Debate Using the NLSY

This paper examines the extent to which differences in welfare generosity across states leads to interstate migration. Using microdata from the National Longitudinal Survey of Youth (NLSY) between 1979 and 1992, we employ a quasi-experimental design that utilizes the categorical eligibility of the welfare system. The pattern of cross-state moves among poor single women with children who are likely to be eligible for benefits is compared to the pattern among other poor households. We find little evidence indicating that welfare-induced migration is a widespread phenomenon.

Discrimination in the Small Business Credit Market

This paper uses data from the 1993 National Survey of Small Business Finances to determine the extent to which minority-owned small businesses face constraints in the credit market beyond those faced by white-owned small businesses. First, we present qualitative evidence indicating that black- and white-owned firms report similar concerns about the factors that may affect their businesses except that blacks are far more likely to report problems with credit availability. Second, we conduct an econometric analysis of loan denial probabilities by race and find that black-owned small businesses are almost three times more likely to have a loan application denied. Even after controlling for the differences in credit-worthiness and other factors that exist between black- and white-owned firms, blacks are still about twice as likely to be denied credit. A series of specification checks indicates that this gap is unlikely to be largely attributed to omitted variable bias. Third, we conduct a similar analysis regarding interest rates charged to approved loans and find black-owned firms pay higher interest rates as well. Finally, even these results are likely to understate differences in credit access because many potential black-owned firms are not in operation due to the lack of credit and those in business may be too afraid to apply. These results indicate that the racial disparity in credit availability is likely caused by discrimination.

Privacy-Preserving Shortest Path Computation

Navigation is one of the most popular cloud computing services. But in virtually all cloud-based navigation systems, the client must reveal her location and destination to the cloud service provider in order to learn the fastest route. In this work, we present a cryptographic protocol for navigation on city streets that provides privacy for both the client's location and the service provider's routing data. Our key ingredient is a novel method for compressing the next-hop routing matrices in networks such as city street maps. Applying our compression method to the map of Los Angeles, for example, we achieve over tenfold reduction in the representation size. In conjunction with other cryptographic techniques, this compressed representation results in an efficient protocol suitable for fully-private real-time navigation on city streets. We demonstrate the practicality of our protocol by benchmarking it on real street map data for major cities such as San Francisco and Washington, D.C.Comment: Extended version of NDSS 2016 pape

Induction and repression of mammalian achaete-scute homologue (MASH) gene expression during neuronal differentiation of P19 embryonal carcinoma cells

MASH1 and MASH2, mammalian homologues of the Drosophila neural determination genes achaete-scute, are members of the basic helix-loop-helix (bHLH) family of transcription factors. We show here that murine P19 embryonal carcinoma cells can be used as a model system to study the regulation and function of these genes. MASH1 and MASH2 display complementary patterns of expression during the retinoic-acid-induced neuronal differentiation of P19 cells. MASH1 mRNA is undetectable in undifferentiated P19 cells but is induced to high levels by retinoic acid coincident with neuronal differentiation. In contrast, MASH2 mRNA is expressed in undifferentiated P19 cells and is repressed by retinoic acid treatment. These complementary expression patterns suggest distinct functions for MASH1 and MASH2 in development, despite their sequence homology. In retinoic-acid-treated P19 cells, MASH1 protein expression precedes and then overlaps expression of neuronal markers. However, MASH1 is expressed by a smaller proportion of cells than expresses such markers. MASH1 immunoreactivity is not detected in differentiated cells displaying a neuronal morphology, suggesting that its expression is transient. These features of MASH1 expression are similar to those observed in vivo, and suggest that P19 cells represent a good model system in which to study the regulation of this gene. Forced expression of MASH1 was achieved in undifferentiated P19 cells by transfection of a cDNA expression construct. The transfected cells expressing exogenous MASH1 protein contained E-box-binding activity that could be super-shifted by an anti-MASH1 antibody, but exhibited no detectable phenotypic changes. Thus, unlike myogenic bHLH genes, such as MyoD, which are sufficient to induce muscle differentiation, expression of MASH1 appears insufficient to promote neurogenesis

The Effect of Medicaid Abortion Funding Restrictions on Abortions, Pregnancies, and Births

This paper considers whether state Medicaid abortion funding restrictions affect the likelihood of getting pregnant, having an abortion, and bearing a child. Aggregate, state-level data and microdata from the National Longitudinal Survey of Youth (NLSY) are applied in the empirical work. Changes in laws resulting from Supreme Court decisions create a natural experiment which is utilized to examine fertility behavior. Multivariate models controlling for state and, in the NLSY, personal characteristics are also estimated using alternative fixed effect specifications. We find that Medicaid funding restrictions are associated with a reduction in both the number of abortions and pregnancies, resulting in either no change or a reduction in births.