Modeling inequality and spread in multiple regression

We consider concepts and models for measuring inequality in the distribution of resources with a focus on how inequality varies as a function of covariates. Lorenz introduced a device for measuring inequality in the distribution of income that indicates how much the incomes below the u$^{th}$ quantile fall short of the egalitarian situation where everyone has the same income. Gini introduced a summary measure of inequality that is the average over u of the difference between the Lorenz curve and its values in the egalitarian case. More generally, measures of inequality are useful for other response variables in addition to income, e.g. wealth, sales, dividends, taxes, market share and test scores. In this paper we show that a generalized van Zwet type dispersion ordering for distributions of positive random variables induces an ordering on the Lorenz curve, the Gini coefficient and other measures of inequality. We use this result and distributional orderings based on transformations of distributions to motivate parametric and semiparametric models whose regression coefficients measure effects of covariates on inequality. In particular, we extend a parametric Pareto regression model to a flexible semiparametric regression model and give partial likelihood estimates of the regression coefficients and a baseline distribution that can be used to construct estimates of the various conditional measures of inequality.Comment: Published at http://dx.doi.org/10.1214/074921706000000428 in the IMS Lecture Notes--Monograph Series (http://www.imstat.org/publications/lecnotes.htm) by the Institute of Mathematical Statistics (http://www.imstat.org

Reference cells and ploidy in the comet assay

In the comet assay single cells are analyzed with respect to their level of DNA damage. Discrimination of the individual cell or cell type based on DNA content, with concomitant scoring of the DNA damage, is useful since this may allow analysis of mixtures of cells. Different cells can then be characterized based on their ploidy, cell cycle stage, or genome size. We here describe two applications of such a cell type-specific comet assay: (i) Testicular cell suspensions, analyzed on the basis of their ploidy during spermatogenesis; and (ii) reference cells in the form of fish erythrocytes which can be included as internal standards to correct for inter-assay variations. With standard fluorochromes used in the comet assay, the total staining signal from each cell – whether damaged or undamaged – was found to be associated with the cell’s DNA content. Analysis of the fluorescence intensity of single cells is straightforward since these data are available in scoring systems based on image analysis. The analysis of testicular cell suspensions provides information on cell type specific composition, susceptibility to genotoxicants, and DNA repair. Internal reference cells, either untreated or carrying defined numbers of lesions induced by ionizing radiation, are useful for investigation of experimental factors that can cause variation in comet assay results, and for routine inclusion in experiments to facilitate standardization of methods, and comparison of comet assay data obtained in different experiments or in different laboratories. They can also be used – in combination with a reference curve – to quantify the DNA lesions induced by a certain treatment. Fish cells of a range of genome sizes, both greater and smaller than human, are suitable for this purpose, and they are inexpensive

Visual evoked potentials in children prenatally exposed to methylmercury

Prenatal exposure to methylmercury can cause both neurobehavioral deficits and neurophysiological changes. However, evidence of neurotoxic effects within the visual nervous system is inconsistent, possibly due to incomplete statistical adjustment for beneficial nutritional factors. We evaluated the effect of prenatal methylmercury exposure on visual evoked potential (VEP) latencies in Faroese children with elevated prenatal methylmercury exposure. A cohort of 182 singleton term births was assembled in the Faroe Islands during 1994–1995. At age 7 years, VEP tracings were obtained from 139 cohort subjects after exclusion of subjects with abnormal vision conditions. We used multiple regression analysis to evaluate the association of mercury concentrations in cord blood and maternal hair at parturition with VEP latencies after adjustment for potential confounders that included the cord-serum phospholipid concentration of n-3 polyunsaturated fatty acids (PUFAs) and the duration of breastfeeding. Unadjusted correlations between mercury exposure and VEP latencies were equivocal. Multiple regression models showed that increased mercury concentrations, especially in maternal hair, were associated with delayed latencies for VEP peak N145. After covariate adjustment, a delay of 2.22 ms (p = 0.02) was seen for each doubling of the mercury concentration in maternal hair. In agreement with neuropsychological findings, the present study suggests that prenatal methylmercury exposure may have an adverse effect on VEP findings despite the absence of clinical toxicity to the visual system. However, this association was apparent only after adjustment for n-3 PUFA status

An Edgeworth expansion for finite population L-statistics

In this paper, we consider the one-term Edgeworth expansion for finite population L-statistics. We provide an explicit formula for the Edgeworth correction term and give sufficient conditions for the validity of the expansion which are expressed in terms of the weight function that defines the statistics and moment conditions.Comment: 14 pages. Minor revisions. Some explanatory comments and a numerical example were added. Lith. Math. J. (to appear

Critical temperature for quenching of pair correlations

The level density at low spin in the 161,162-Dy and 171,172-Yb nuclei has been extracted from primary gamma rays. The nuclear heat capacity is deduced within the framework of the canonical ensemble. The heat capacity exhibits an S-formed shape as a function of temperature, which is interpreted as a fingerprint of the phase transition from a strongly correlated to an uncorrelated phase. The critical temperature for the quenching of pair correlations is found at Tc=0.50(4) MeV.Comment: 8 pages including 4 figures, different method to extract Tc, different figures, text partly rewritte

Inflammation markers in multiple sclerosis: CXCL16 reflects and may also predict disease activity

Background: Serum markers of inflammation are candidate biomarkers in multiple sclerosis (MS). ω-3 fatty acids are suggested to have anti-inflammatory properties that might be beneficial in MS. We aimed to explore the relationship between serum levels of inflammation markers and MRI activity in patients with relapsing remitting MS, as well as the effect of ω-3 fatty acids on these markers. Methods: We performed a prospective cohort study in 85 relapsing remitting MS patients who participated in a randomized clinical trial of ω-3 fatty acids versus placebo (the OFAMS study). During a period of 24 months 12 repeated magnetic resonance imaging (MRI) scans and nine serum samples were obtained. We measured 10 inflammation markers, including general down-stream markers of inflammation, specific markers of up-stream inflammatory pathways, endothelial action, and matrix regulation. Results: After Bonferroni correction, increasing serum levels of CXCL16 and osteoprotegerin were associated with low odds ratio for simultaneous MRI activity, whereas a positive association was observed for matrix metalloproteinase (MMP) 9. CXCL16 were also associated with low MRI activity the next month, but this was not significant after Bonferroni correction. In agreement with previously reported MRI and clinical results, ω-3 fatty acid treatment did not induce any change in the inflammation markers. Conclusions: Serum levels of CXCL16, MMP-9, and osteoprotegerin reflect disease activity in MS, but are not affected by ω-3 fatty acid treatment. CXCL16 could be a novel biomarker and potential predictor of disease activity in MS.© 2013 Holmøy et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited

Den konjunkturpolitiske handlefridomen i finanspolitikken

I moderne finanspolitisk litteratur er det vanleg å gå ut frå at statsfinansane skal spele ei viktig rolle i konjunkturpolitikken, dvs. i dei offentlege freistnadene på å få til ein etterspurnad etter varer og tenester som til kvar tid er stor nok, men ikkje større, enn det som trengst for å skape full sysselsetting og tilstrekkeleg høg utnytting av produksjonsutstyret. 2 ) Denne rolla blir i finansteorien og endå meir i numeriske makro-økonomiske modellar, studert under førsetnad av at det offentlege er ei avgjerdseining som etter måten fritt kan fastsette storleiken av sine styringsvariable. 3) Vanlegvis ser ein bort frå at vi har ei funksjonsdeling mellom sentrale og lokale styresmakter, at avgjerder jamvel innanfor statsadministrasjonen i stor monn er desentraliserte, at eit stort kompleks av lovreglar, stortingsvedtak, avtaler av ymse slag, fråsegner frå storting og regjering og meir eller mindre fast sedvane legg band på finanspolitikken og endeleg at den måten som vedtak blir til og sett iverk på, skil seg mye frå det enkle «å velje storleiken av dei styringsvariable», mellom anna fordi demokratiske statar har ei politisk maktfordeling og ein tingingsstrategi for løysing av interessekonfliktar, der politiske parti og organisasjonar av ymse slag spelar ei viktig rolle

Eksperimentell dynamisk analyse av et trebasert komposittdekke En evaluering av dempingskoeffisient, egenfrekvenser og egenmoder

Denne masteroppgaven inngår som en del av forskningsprosjektet DynaTTB, som skal kartlegge dempingsegenskaper for høyhus i tre. Opprinnelig tilhørte denne oppgaven arbeidspakke 2, som omhandler eksperimentelle forsøk på komponenter av tre. I denne oppgaven ble det gjort omfattende dynamiske forsøk på et komposittdekke som var fritt opplagt i hjørnene. Etter innhenting av måledata ble det beregnet demping på hele tre ulike måter. Arbeidet med denne avhandlingen ble en videreføring av arbeidet gjort i prosjektoppgaven foregående høst, der de dynamiske egenskapene til et annet gulv ble evaluert. Det ble tidlig modellert enkle Abaqus-modeller og gjort innledende forsøk med slaghammer (engelsk: modal hammer/impact hammer) som et grunnlag for videre forsøk og modellering. Tredekket ble modellert med S4R-skallelementer i Abaqus/CAE. Det ble også antatt fullt samvirke mellom bjelkestegene og topp- og bunnplate. Disse analysene ga resultater som stemte veldig godt med laboratorieresultatene for første og andre mode. Siden protokollen i laboratorieforsøkene var å tilføre masse på midtspenn av dekket og gjøre dynamiske forsøk for alle massetrinn ble også denne metodikken implementert i Abaqus. For økt masse beregnet modellen korrekte egenfrekvenser for første og andre mode, mens presisjonen ble betydelig lavere for høyere moder. For analyse av steady state-akselerasjoner under tvungne vibrasjoner ga Abaqus-analysen også rimelig gode resultater. Fra forsøk med ANCO-vibrator ved belastning på resonans med første egenfrekvens ble demping beregnet fra logaritmisk dekrement og kurvetilpasning på frekvens-respons-funksjonen. Dette ga dempingsverdier mellom 0,48 % og 0,95 %. De dempede frie vibrasjonene viste tegn til minkende demping for økt masse, samt tydelig minkende demping for minkende akselerasjonsamplituder. Dempingstallene for tvungne vibrasjoner varierte mer, men viste ingen klare tendenser i retning av masse- eller amplitudeavhengighet. Forsøk med slaghammer ga konsekvent demping mellom 0,62 % og 0,68 % for første mode, og økende demping for høyere moder. For slaghammer var det kun en av fire egenfrekvenser under 50 Hz som hadde økt demping for økende masse. Samtidig var det kun første og andre egenfrekvens som minket med økt masse på midtspenn. Funnene fra dette arbeidet stemte godt overens med tidligere arbeid utført på det samme gulvet i 2017. Basert på erfaringer fra dette arbeidet og protokollen benyttet for de eksperimentelle forsøkene ble det utarbeidet et forslag til prosedyre for lignende forsøk i fremtiden.This Master’s Thesis is a part of the research project DynaTTB, which aims to better understand damping of high-rise timber buildings. This thesis originally belonged to work package 2, which contains experimental research on components and assemblies of timber. During the work with this thesis extensive dynamic experiments were carried out on a composite floor, simply supported in all corners. Subsequently, three methods for calculating damping was applied. During the Project Thesis the previous semester, a dynamic analysis of another wooden composite floor was carried out. Due to earlier experiences gained through the Project Thesis, simple Abaqus models and initial experiments with the impact hammer was executed to form a foundation for further work. The timber floor was modelled with S4R shell elements in Abaqus/CAE. Furthermore, it was assumed full composite action between the webs and the flanges. For the first and the second modes of vibration the Abaqus models showed good agreements with the experimental results. During the lab experiments mass was added to the midspan of the floor, and therefore this method was implemented in Abaqus. For the increased mass the first and second eigenfrequency was calculated with good precision, whereas the precision decreased significantly for higher modes. The analysis of steady state accelerations under forced vibrations also showed satisfactory results. From the experiments with the ANCO vibrator loading at resonance with the first eigen-frequency, damping was calculated from both logarithmic decrement and a curve fit on the frequency response function. This revealed damping values between 0,48 % and 0,95 %. The damped free vibrations showed signs of decreasing damping for increased mass, and clear signs of smaller damping for smaller amplitudes of acceleration. During forced vibrations, the damping had bigger deviations but revealed no clear dependency on neither mass nor acceleration amplitudes. For the Modal Hammer, a damping ration between 0,62 % and 0,68 % was measured for the first mode, with increasing damping for higher modes. Only one out of four eigenfrequencies below 50 Hz got higher damping for increased mass. At the same time, only the first and the second eigenfrequency were decreasing for increased mass. These findings correspond well with the previous work carried out in 2017. Based on the experiences from this experimental work, a procedure for future work is proposed