Abstract: One in twelve Americans suffers from asthma and its annual costs are estimated to exceed $50 billion. Simultaneously, the root causes of the disease remain unknown. A recent hypothesis speculates that maternal vitamin D levels during pregnancy affect the probability the fetus later develops asthma. In two large-scale studies, we test this hypothesis using a natural experiment afforded by historical variation in sunlight, a major source of vitamin D. Specifically, holding the birth location and month fixed, we see how exogenous within-location variation in sunlight across birth years affects the probability of asthma onset. We show that this measurement of sunlight correlates with actual exposure, and consistent with pre-existing results from the fetal development literature, we find substantial and highly significant evidence in both datasets that increased sunlight during the second trimester lowers the subsequent probability of asthma. Our results suggest policies designed to augment vitamin D levels in pregnant women, the large majority of whom are vitamin D insufficient, could be very cost-effective.
Abstract: People often favor members of their own group, while discriminating against members of other groups. Such in-group favoritism has been shown to play an important role in human cooperation. However, in the face of changing conflicts and shifting alliances, it is essential for group identities to be flexible. Using the dictator game from behavioral economics, we demonstrate the remodeling of group identities among supporters of Democratic presidential candidates Barack Obama and Hillary Clinton. After Clinton's concession in June 2008, Democrats were more generous toward supporters of their own preferred candidate than to supporters of the other Democratic candidate. The bias observed in June persisted into August, and disappeared only in early September after the Democratic National Convention. We also observe a strong gender effect, with bias both appearing and subsiding among men only. This experimental study illustrates a dynamic change in bias, tracking the realignment of real world conflict lines and public efforts to reconstitute group identity. The change in salient group identity we describe here likely contributed to the victory of Barack Obama in the 2008 presidential election.
Abstract: We explore how risk-taking in the card game contract bridge, and in a financial gamble, correlate with variation in the dopamine receptor D4 gene (DRD4) among serious tournament bridge players. In bridge risk-taking, we find significant interactions between genetic predisposition and skill. Among men with the 7-repeat allele of DRD4, namely 7R+ men, those with more bridge skill take more good risks and fewer bad risks, while the opposite is found for less-expert 7R+ men. Conversely, skill does not predict risk-taking among men without the 7R+ allele. Consistent with some prior studies, we also find that 7R+ men take more risk in the financial gamble. We find no relationship between 7R+ and either risk measure among our female subjects. Our results suggest that the dopamine system plays an important role in individual differences in risk-taking among men, and is the first to distinguish between advantageous and disadvantageous risk-taking.
Theoretical contract theory paper on extracting natural resources in countries where there is a high risk of expropriation.