Inconsistency of the MLE for the joint distribution of interval censored survival times and continuous marks

This paper considers the nonparametric maximum likelihood estimator (MLE) for the joint distribution function of an interval censored survival time and a continuous mark variable. We provide a new explicit formula for the MLE in this problem. We use this formula and the mark specific cumulative hazard function of Huang and Louis (1998) to obtain the almost sure limit of the MLE. This result leads to necessary and sufficient conditions for consistency of the MLE which imply that the MLE is inconsistent in general. We show that the inconsistency can be repaired by discretizing the marks. Our theoretical results are supported by simulations.Comment: 27 pages, 4 figure

Electric/magnetic reciprocity in premetric electrodynamics with and without magnetic charge, and the complex electromagnetic field

We extend an axiomatic approach to classical electrodynamics, which we developed recently, to the case of non-vanishing magnetic charge. Then two axioms, namely those of the existence of the Lorentz force (Axiom 2) and of magnetic flux conservation (Axiom 3) have to be generalized. Electric/magnetic reciprocity constitutes a guiding principle for this undertaking. The extension of the axioms can be implemented at a premetric stage, i.e., when metric and connection of spacetime don't play a role. Complex Riemann-Silberstein fields of the form $(E\pm i {\cal H},{\cal D}\pm i B)$ have a natural place in the theory, independent of the Hodge duality mapping defined by any particular metric.Comment: 13 pages in latex, 3 references added, text slightly revise

Survival Benefit-Based Deceased-Donor Liver Allocation

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/74806/1/j.1600-6143.2009.02571.x.pd

Ovine reference materials and assays for prion genetic testing

<p>Abstract</p> <p>Background</p> <p>Genetic predisposition to scrapie in sheep is associated with several variations in the peptide sequence of the prion protein gene (<it>PRNP</it>). DNA-based tests for scoring <it>PRNP </it>codons are essential tools for eradicating scrapie and for evaluating rare alleles for increased resistance to disease. In addition to those associated with scrapie, there are dozens more <it>PRNP </it>polymorphisms that may occur in various flocks. If not accounted for, these sites may cause base-pair mismatching with oligonucleotides used in DNA testing. Thus, the fidelity of scrapie genetic testing is enhanced by knowing the position and frequency of <it>PRNP </it>polymorphisms in targeted flocks.</p> <p>Results</p> <p>An adaptive DNA sequencing strategy was developed to determine the 771 bp <it>PRNP </it>coding sequence for any sheep and thereby produce a consensus sequence for targeted flocks. The strategy initially accounted for 43 known polymorphisms and facilitates the detection of unknown polymorphisms through an overlapping amplicon design. The strategy was applied to 953 sheep DNAs from multiple breeds in U.S. populations. The samples included two sets of reference sheep: one set for standardizing <it>PRNP </it>genetic testing and another set for discovering polymorphisms, estimating allele frequencies, and determining haplotype phase. DNA sequencing revealed 16 previously unreported polymorphisms, including a L237P variant on the F₁₄₁haplotype. Two mass spectrometry multiplex assays were developed to score five codons of interest in U.S. sheep: 112, 136, 141, 154, and 171. Reference tissues, DNA, trace files, and genotypes from this project are publicly available for use without restriction.</p> <p>Conclusion</p> <p>Identifying ovine <it>PRNP </it>polymorphisms in targeted flocks is critical for designing efficient scrapie genetic testing systems. Together with reference DNA panels, this information facilitates training, certification, and development of new tests and knowledge that may expedite the eradication of sheep scrapie.</p

Limits on Production of Magnetic Monopoles Utilizing Samples from the DO and CDF Detectors at the Tevatron

We present 90% confidence level limits on magnetic monopole production at the Fermilab Tevatron from three sets of samples obtained from the D0 and CDF detectors each exposed to a proton-antiproton luminosity of $\sim175 {pb}^{-1}$ (experiment E-882). Limits are obtained for the production cross-sections and masses for low-mass accelerator-produced pointlike Dirac monopoles trapped and bound in material surrounding the D0 and CDF collision regions. In the absence of a complete quantum field theory of magnetic charge, we estimate these limits on the basis of a Drell-Yan model. These results (for magnetic charge values of 1, 2, 3, and 6 times the minimum Dirac charge) extend and improve previously published bounds.Comment: 18 pages, 17 figures, REVTeX

Planning for Uncertainty and Fallbacks Can Increase the Number of Transplants in a Kidney‐Paired Donation Program

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/113739/1/ajt13413.pd

Risk-Adjusted Survival after Coronary Artery Bypass Grafting: Implications for Quality Improvement

Mortality represents an important outcome measure following coronary artery bypass grafting. Shorter survival times may reflect poor surgical quality and an increased number of costly postoperative complications. Quality control efforts aimed at increasing survival times may be misleading if not properly adjusted for case-mix severity. This paper demonstrates how to construct and cross-validate efficiency-outcome plots for a specified time (e.g., 6-month and 1-year survival) after coronary artery bypass grafting, accounting for baseline cardiovascular risk factors. The application of this approach to regional centers allows for the localization of risk stratification rather than applying overly broad and non-specific models to their patient populations

Semiparametric estimation of the accelerated failure time model with partly interval-censored data

Partly interval-censored (PIC) data arise when some failure times are exactly observed while others are only known to lie within certain intervals. In this article, we consider efficient semiparametric estimation of the accelerated failure time (AFT) model with PIC data. We first generalize the Buckley–James estimator for right-censored data to PIC data. Then, we develop a one-step estimator by deriving and estimating the efficient score for the regression parameters. We show that under mild regularity conditions the generalized Buckley–James estimator is consistent and asymptotically normal and the one-step estimator is consistent and asymptotically normal with a covariance matrix that attains the semiparametric efficiency bound. We conduct extensive simulation studies to examine the performance of the proposed estimators in finite samples and apply our methods to data derived from an AIDS study

Improved Experimental Limits on the Production of Magnetic Monopoles

We present new limits on low mass accelerator-produced point-like Dirac magnetic monopoles trapped and bound in matter surrounding the D\O collision region of the Tevatron at Fermilab (experiment E-882). In the context of a Drell-Yan mechanism, we obtain cross section limits for the production of monopoles with magnetic charge values of 1, 2, 3, and 6 times the minimum Dirac charge of the order of picobarns, some hundred times smaller than found in similar previous Fermilab searches. Mass limits inferred from these cross section limits are presented.Comment: 5 pages, 4 eps figures, REVTe