Could It Be Better to Discard 90% of the Data? A Statistical Paradox

Conventional practice is to draw inferences from all available data and research results, even though there is ample evidence to suggest that empirical literatures suffer from publication selection bias. When a scientific literature is plagued by such bias, a simple discarding of the vast majority of empirical results can actually improve statistical inference and estimation. Simulations demonstrate that, if the majority of researchers, reviewers, and editors use statistical significance as a criterion for reporting or publishing an estimate, discarding 90% of the published findings greatly reduces publication selection bias and is often more efficient than conventional summary statistics. Improving statistical estimation and inference through removing so much data goes against statistical theory and practice; hence, it is paradoxical. We investigate a very simple method to reduce the effects of publication bias and to improve the efficiency of summary estimates of accumulated empirical research results that averages the most precise ten percent of the reported estimates (i.e., ‘Top10’). In the process, the critical importance of precision (the inverse of an estimate’s standard error) as a measure of a study’s quality is brought to light. Reviewers and journal editors should use precision as one objective measure of a study’s quality.Publication Selection, Meta-analysis, Precision, Simulations, Meta-Regression.

Gap States in Dilute Magnetic Alloy Superconductors

We study states in the superconducting gap induced by magnetic impurities using self-consistent quantum Monte Carlo with maximum entropy and formally exact analytic continuation methods. The magnetic impurity susceptibility has different characteristics for T_{0} \alt T_{c0} and T_{0} \agt T_{c0} ($T_{0}$: Kondo temperature, $T_{c0}$: superconducting transition temperature) due to the crossover between a doublet and a singlet ground state. We systematically study the location and the weight of the gap states and the gap parameter as a function of $T_{0}/T_{c0}$ and the concentration of the impurities.Comment: 4 pages in ReVTeX including 4 encapsulated Postscript figure

Village health volunteers: key issues facing agencies in Malawi

In March 1991 the International Eye Foundation and Adventist Development Be Relief Agency conducted a workshop on village health volunteers, bringing together representatives from Malawibased non-governmental organizations, the Ministry of Health, and USAID. The participants discussed recruitment, training, rewards, retention, and roles of village health volunteers. This paper presents background data on village health volunteers in Malawi and elsewhere and reviews the key issues facing health care providers in working with village health volunteers. A copy of the workshop report can be obtained from IEF or ADRA

Systematic study of d-wave superconductivity in the 2D repulsive Hubbard model

The cluster size dependence of superconductivity in the conventional two-dimensional Hubbard model, commonly believed to describe high-temperature superconductors, is systematically studied using the Dynamical Cluster Approximation and Quantum Monte Carlo simulations as cluster solver. Due to the non-locality of the d-wave superconducting order parameter, the results on small clusters show large size and geometry effects. In large enough clusters, the results are independent of the cluster size and display a finite temperature instability to d-wave superconductivity.Comment: 4 pages, 3 figures; updated with version published in PRL; added values of Tc obtained from fit

Biosynthesis and Role of N-Linked Glycosylation in Cell Surface Structures of Archaea with a Focus on Flagella and S Layers

The genetics and biochemistry of the N-linked glycosylation system of Archaea have been investigated over the past 5 years using flagellins and S layers as reporter proteins in the model organisms, Methanococcus voltae, Methanococcus maripaludis, and Haloferax volcanii. Structures of archaeal N-linked glycans have indicated a variety of linking sugars as well as unique sugar components. In M. voltae, M. maripaludis, and H. volcanii, a number of archaeal glycosylation genes (agl) have been identified by deletion and complementation studies. These include many of the glycosyltransferases and the oligosaccharyltransferase needed to assemble the glycans as well as some of the genes encoding enzymes required for the biosynthesis of the sugars themselves. The N-linked glycosylation system is not essential for any of M. voltae, M. maripaludis, or H. volcanii, as demonstrated by the successful isolation of mutants carrying deletions in the oligosaccharyltransferase gene aglB (a homologue of the eukaryotic Stt3 subunit of the oligosaccharyltransferase complex). However, mutations that affect the glycan structure have serious effects on both flagellation and S layer function

Baseball Card Pricing Model: A Demonstration with Well-known Players

A simple hedonic pricing model is developed for baseball cards, of the type often used successfully to model prices for artworks. The model is estimated for a dataset of twelve well-known players observed at eight points in time over a span of twenty years. Dummy variables are used to capture various relevant characteristics of the player or card. This model was estimated separately for two different approaches or assumptions about rates of return. Estimates perform extremely well, explaining most differences among baseball card prices for the cards in the sample. Among extrinsic variables that represent specific players and card characteristics that differentiate cards issued during the same season, race had a significant positive effect on price for black players. Batting average and number of World Series appearances had significant positive impacts on price, but surprisingly, rookie cards tended to be worth relatively less than non-rookie cards. Similarly unexpected findings with respect to players\u27 death and elevation to the Hall of Fame may result from trying to estimate too many characteristics simultaneously on a limited dataset. Results suggest famous players\u27 cards generally are extremely attractive investment instruments

Two-Channel Kondo Lattice: An Incoherent Metal

The two-channel Kondo lattice model is examined with a Quantum Monte Carlo simulation in the limit of infinite dimensions. We find non-fermi-liquid behavior at low temperatures including a finite low-temperature single-particle scattering rate, the lack of a fermi edge and Drude weight. However, the low-energy density of electronic states is finite. Thus, we identify this system as an incoherent metal. We discuss the relevance of our results for concentrated heavy fermion metals with non-Fermi-Liquid behavior.Comment: LaTex, 5 pages, 3 Postscript files. Revision - in reference 5 and 6(a

Dynamics of disordered heavy Fermion systems

Dynamics of the disordered heavy Fermion model of Dobrosavljevic et al. are calculated using an expression for the spectral function of the Anderson model which is consistent with quantum Monte Carlo results. We compute the self-energy for three distributions of Kondo scales including the distribution of Bernal et al. for UCu{5-x}Pd{x}. The corresponding low temperature optical conductivity shows a low-frequency pseudogap, a negative optical mass enhancement, and a linear in frequency transport scattering rate, consistent with results in Y{1-x}U{x}Pd{3} and UCu{5-x}Pd{x}.Comment: 5 pages, LaTeX and 4 PS figure