Instrumental variables estimation with flexible distribution

Instrumental variables are often associated with low estimator precision. This paper explores efficiency gains which might be achievable using moment conditions which are nonlinear in the disturbances and are based on flexible parametric families for error distributions. We show that these estimators can achieve the semiparametric efficiency bound when the true error distribution is a member of the parametric family. Monte Carlo simulations demonstrate low efficiency loss in the case of normal error distributions and potentially significant efficiency improvements in the case of thick-tailed and/or skewed error distributions.

Latest Development of the Interstate Commerce Power

The litigation under the anti-lottery act of 1895, has for the first time raised the important constitutional question whether congress, under its general power to regulate interstate commerce, can select any particular article and exclude it from interstate commerce altogether-whether the power to regulate involves the power to prohibit. For nearly a century after the foundation of the government no attempt was made by congress to restrict interstate commerce by excluding any article therefrom. Quarantine legislation, however, opened the way, and the anti-lottery act sharply raised the question of power. Lottery tickets in the earliest days of the republic were the subjects of lawful and popular, and even pious traffic. They were among the most universal means of raising money. They built churches, schools and colleges. They were used by the United States government itself as a fiscal agency. Bold would have been the man who would dare predict what has, however, happened-that lottery tickets in a century would be regarded by the great majority of the people as an evil, and would be prohibited by the legislature of almost every state. Congress first excluded them from the mails, and this, after much litigation, was sustained under the general power to conduct the mails. Congress next, in 1895, took a more radical step and excluded them from interstate commerce altogether. This raised two interesting questions under the power to regulate commerce; first, whether a lottery ticket is an article of commerce at all; and second, whether the power to regulate commerce implies the power to prohibit it

Siderophore production by heterotrophic bacterial isolates from the Costa Rica Upwelling Dome

Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution June 2008.An increased understanding of heterotrophic bacterial strategies for acquiring nutrients and trace elements is critical for elucidating their impact on biogeochemical cycling in the ocean. It is estimated that iron is a limiting nutrient for phytoplankton growth in over 30% of the open ocean, but still little is known about bacterial strategies for iron acquisition. Siderophore (Fe ligand) production by bacteria may play a major role in influencing the bioavailability of iron in the ocean. Despite the importance of siderophores in the environment, only limited information from a select group of bacteria is available. On a cruise through the Costa Rica Dome (CRD) upwelling region in July 2005, a library of 867 isolates from five depth profiles inside and outside of the dome was obtained and screened for siderophore production using the Chrome Azurol-S (CAS) assay. Phylogenetic affiliation of 134 isolates was determined by sequencing the 16s rDNA gene, and determined that gamma proteobacteria such as Alteromonas, Pseudoalteromonas, Halomonas, and Marinobacter dominated the collection, while alpha-proteobacteria such as Roseobacter were also represented. The isolates obtained from stations in the CRD showed greater siderophore-producing capabilities between 55m and 100m while strains isolated from outside the CRD had shallower peak (~8-35m) production. Functional group determination showed that hydroxamate production dominated from 50-150m, while hydroxamate and catechol production is roughly equal in shallower waters. By characterizing the siderophores produced by these isolates and determining the genetic make-up of the population, these findings further our understanding of how heterotrophic microbes affect biogeochemical processes and the competitive nature of nutrient acquisition.I am grateful to my funding sources, National Science Foundation grants BO OCE- 0352241 "The Effect of Iron Bioavailability on Synechococcus diversity from a HNLC region to the Costa Rica upwelling dome" and CO-OCE-0452883 "Interactions of Cobalt and Iron with in situ Cyanobacterial Physiology in the South Atlantic and the Benguela Upwelling Region", the National Science Foundation Graduate Research Fellowship, and the Academic Programs office

Doctrine of Stare Decisis

I am requested to present a paper whose theme is suggested by the Present Problems of Private Law, as distinguished from law that has a constitutional or international aspect. I doubt whether there is any other section of the Congress whose themes are so difficult to select. We cover, indeed, those branches that mainly concern the ordinary, plain, steady-going, stay-at-home, law-abiding citizen,-that multitude of questions among which most legal practitioners everywhere are wearing out their lives; working every day and all day upon Present Problems of Private Law. Each of those problems interests the parties to the particular litigation or negotiation or dispute or difficulty which brings it up. Some interest even the lawyers to whom they are presented. Few interest anybody else; and even among these few but a small minority possess such worldwide interest that they are worthy of the consideration of a Congress representing all the civilized nations of the globe. Furthermore, this is not an International Congress of Lawyers. There is such a Congress; but it is a different one, and does not meet until next week. This is a Congress of Arts and Science; and of all the Present Problems of Private Law none is so difficult as to give to any portion of Private Law, as known at least to the American practitioner, the semblance either of a Science or of an Art