Bayesian variable selection using cost-adjusted BIC, with application to cost-effective measurement of quality of health care

In the field of quality of health care measurement, one approach to assessing patient sickness at admission involves a logistic regression of mortality within 30 days of admission on a fairly large number of sickness indicators (on the order of 100) to construct a sickness scale, employing classical variable selection methods to find an ``optimal'' subset of 10--20 indicators. Such ``benefit-only'' methods ignore the considerable differences among the sickness indicators in cost of data collection, an issue that is crucial when admission sickness is used to drive programs (now implemented or under consideration in several countries, including the U.S. and U.K.) that attempt to identify substandard hospitals by comparing observed and expected mortality rates (given admission sickness). When both data-collection cost and accuracy of prediction of 30-day mortality are considered, a large variable-selection problem arises in which costly variables that do not predict well enough should be omitted from the final scale. In this paper (a) we develop a method for solving this problem based on posterior model odds, arising from a prior distribution that (1) accounts for the cost of each variable and (2) results in a set of posterior model probabilities that corresponds to a generalized cost-adjusted version of the Bayesian information criterion (BIC), and (b) we compare this method with a decision-theoretic cost-benefit approach based on maximizing expected utility. We use reversible-jump Markov chain Monte Carlo (RJMCMC) methods to search the model space, and we check the stability of our findings with two variants of the MCMC model composition ($\mathit{MC}^3$) algorithm.Comment: Published in at http://dx.doi.org/10.1214/08-AOAS207 the Annals of Applied Statistics (http://www.imstat.org/aoas/) by the Institute of Mathematical Statistics (http://www.imstat.org

The entry of diphtheria toxin into the mammalian cell cytoplasm: evidence for lysosomal involvement

Lysosomotropic amines, such as ammonium chloride, are known to protect cells from the cytotoxic effects of diphtheria toxin. These drugs are believed to inhibit the transport of the toxin from a receptor at the cell exterior into the cytoplasm where a fragment of the toxin arrests protein synthesis. We studied the effects of lysosomotropic agents on the cytotoxic process to better understand how the toxin enters the cytoplasm. The cytotoxic effects of diphtheria toxin were not inhibited by antitoxin when cells were preincubated at 37 degrees C with toxin and ammonium chloride, exposed to antitoxin at 4 degrees C, washed to relieve the ammonium chloride inhibition, and finally warmed to 37 degrees C. The antigenic determinants of the toxin were, therefore, either altered or sheltered. It is likely that the combination of ammonium chloride and a low temperature trapped the toxin in an intracellular vesicle from which the toxin could proceed to the cytoplasm. Because lysosomotropic amines raise the pH within acidic intracellular vesicles, such as lysosomes, they could trap the toxin within such a vesicle if an acidic environment were necessary for the toxin to penetrate into the cytoplasm. We simulated acidic conditions which the toxin might encounter by exposing cells with toxin bound to their surface to acidic medium. We then measured the effects of lysosomotropic amines on the activity of the toxin to see if the acidic environment substituted for the function normally inhibited by the drugs. The drugs no longer protected the cells. This suggests that exposing the toxin to an acidic environment, such as that found within lysosomes, is an important step in the penetration of diphtheria toxin into the cytoplasm

Bulletin No. 361 - How Much Barley for Turkeys

During recent years high energy turkey diets containing com as the sole source of ground grain have been fed extensively. Corn has been used as the grain part of the mash because of its high energy, low fiber qualities, and because its deficiencies in amino acids, vitamins, and minerals have been determined by research. Supplements to overcome these deficiencies have been added to high energy corn diets. Excellent results have been obtained when adequate supplementation of vitamins, amino acids, and minerals were made. In this area frequent inquiries are made as to the possibilities of substituting barley for part or all of the corn. These inquiries are undoubtedly made because barley is generally cheaper than corn. It is a product that is grown locally and yields are above other grains on local irrigated farms. Poley and Wilson found no appreciable differences in the rate of growth when turkeys received either corn, wheat, oats, or barley in growing rations. No soybean oil meal was fed as a protein concentrate in their feeding trials. However, since their investigation, new vitamins necessary for growth have been discovered. Alder found that barley could replace a large part of corn in the turkey diet. However, all barley diets were not included in his investigations. The objectives of this investigation were to study the effects of substituting ground barley for ground corn on a pound for pound basis in the turkey growing mash

Pion Decay Constant, ZAZ_A and Chiral Log from Overlap Fermions

We report our calculation of the pion decay constant $f_\pi$, the axial renormalization constant $Z_A$, and the quenched chiral logarithms from the overlap fermions. The calculation is done on a quenched $20^4$ lattice at $a=0.148$ fm using tree level tadpole improved gauge action. The smallest pion mass we reach is about 280 MeV. The lattice size is about 4 times the Compton wavelength of the lowest mass pion.Comment: Lattice2001(Hadronic Matrix Elements), 3pages, 5figure

Chiral Properties of Pseudoscalar Mesons on a Quenched 20420^4 Lattice with Overlap Fermions

The chiral properties of the pseudoscalar mesons are studied numerically on a quenched $20^4$ lattice with the overlap fermion. We elucidate the role of the zero modes in the meson propagators, particularly that of the pseudoscalar meson. The non-perturbative renormalization constant $Z_A$ is determined from the axial Ward identity and is found to be almost independent of the quark mass for the range of quark masses we study; this implies that the $O(a^2)$ error is small. The pion decay constant, $f_{\pi}$, is calculated from which we determine the lattice spacing to be 0.148 fm. We look for quenched chiral log in the pseudoscalar decay constants and the pseudoscalar masses and we find clear evidence for its presence. The chiral log parameter $\delta$ is determined to be in the range 0.15 -- 0.4 which is consistent with that predicted from quenched chiral perturbation theory.Comment: Version accepted for publication by PRD. A few minor typographical errors have been corrected. 24 pages, 11 figure

Enriched surface acidity for surfactant-free suspensions of carboxylated carbon nanotubes purified by centrifugation

AbstractIt is well known that surfactant-suspended carbon nanotube (CNT) samples can be purified by centrifugation to decrease agglomerates and increase individually-dispersed CNTs. However, centrifugation is not always part of protocols to prepare CNT samples used in biomedical applications. Herein, using carboxylated multi-walled CNTs (cMWCNTs) suspended in water without a surfactant, we developed a Boehm titrimetric method for the analysis of centrifuged cMWCNT suspensions and used it to show that the surface acidity of oxidized carbon materials in aqueous cMWCNT suspensions was enriched by ∼40% by a single low-speed centrifugation step. This significant difference in surface acidity between un-centrifuged and centrifuged cMWCNT suspensions has not been previously appreciated and is important because the degree of surface acidity is known to affect the interactions of cMWCNTs with biological systems