Class Size and Class Heterogeneity

We study how class size and composition affect the academic and labor market performances of college students, two crucial policy questions given the secular increase in college enrollment. We rely on the random assignment of students to teaching classes. Our results suggest that a one standard deviation increase in the class-size would result in a 0.1 standard deviation deterioration of the average grade. Further, the effect is heterogenous as female and higher income students seem almost immune to the size of the class. Also, the effects on performance of class composition in terms of gender and ability appears to be inverse U-shaped. Finally, a reduction of 20 students (one standard deviation) in one's class size has a positive effect on monthly wages of about 80 Euros (115 USD) or 6% over the average.class size, heterogeneity, experimental evidence, academic performance, wages

How does Risk-selection Respond to Risk-adjustment? Evidence from the Medicare Advantage Program

Medicare administers a traditional public fee-for-service (FFS) plan while also allowing enrolles to join government-funded private Medicare Advantage (MA) plans.We model how selection and differential payments - the value of the capitation payments the firm receives to insure an individual minus the counterfactual cost of his coverage in FFS - change after the introduction of a comprehensive risk adjustment formula in 2004. Our model predicts that firm screening efforts along dimensions included in the model ("extensive-margin" selection) should fall, whereas screening efforts along dimensions excluded ("intensive-margin" selection) should increase. These endogenous responses to the risk-adjustment formula can in fact lead differential payments to increase. Using individual-level administrative data on Medicare enrollees from 1994 to 2006, we show that while MA enrollees are positively selected throughout the sample period, after risk adjustment extensive-margin selection decreases whereas intensive-margin selection increases. We find that differential payments actually rise after risk-adjustment, and estimate that they totaled $23 billion in 2006, or about six percent of total Medicare spending.Health Care Markets

Improving formaldehyde consumption drives methanol assimilation in engineered E. coli

Due to volatile sugar prices, the food vs fuel debate, and recent increases in the supply of natural gas, methanol has emerged as a promising feedstock for the bio-based economy. However, attempts to engineer Escherichia coli to metabolize methanol have achieved limited success. Here, we provide a rigorous systematic analysis of several potential pathway bottlenecks. We show that regeneration of ribulose 5-phosphate in E. coli is insufficient to sustain methanol assimilation, and overcome this by activating the sedoheptulose bisphosphatase variant of the ribulose monophosphate pathway. By leveraging the kinetic isotope effect associated with deuterated methanol as a chemical probe, we further demonstrate that under these conditions overall pathway flux is kinetically limited by methanol dehydrogenase. Finally, we identify NADH as a potent kinetic inhibitor of this enzyme. These results provide direction for future engineering strategies to improve methanol utilization, and underscore the value of chemical biology methodologies in metabolic engineering