arXiv subjects

Martin Schumacher

Publications and source records attributed to Martin Schumacher.

At least 19 recordsLinked to original sources

arXiv2026

Temporal Trends in Incidence of Dementia in a Birth Cohorts Analysis of the Framingham Heart Study

Background: Dementia leads to a high burden of disability and the number of dementia patients worldwide doubled between 1990 and 2016. Nevertheless, some studies indicated a decrease in dementia risk which may be due to a bias caused by conventional analysis methods that do not adequately account for missing disease information due to death. Methods: This study re-examines potential trends in dementia incidence over four decades in the Framingham Heart Study. We apply a multistate modeling framework tailored to interval-censored illness-death data and define three non-overlapping birth cohorts (1915-1924, 1925-1934, and 1935-1944). Trends are evaluated based on both dementia prevalence and dementia risk, using age as the underlying timescale. Additionally, age-conditional dementia probabilities stratified by sex are estimated. Results: A total of 731 out of 3828 individuals were diagnosed with dementia. The multistate model analysis revealed no temporal decline in dementia risk across birth cohorts, irrespective of sex. When stratified by sex and adjusted for education, women consistently exhibited higher lifetime age-conditional risks (46%-50%) than men (30%-34%) over the study period. Conclusions: We recommend using a combination of multistate approach and separation into birth cohorts to adequately estimate trends of disease risk in cohort studies as well as to communicate patient-relevant outcomes such age-conditional disease risks.

stat.AP↗

arXiv2019

Polarizability of the nucleon

The status of the experimental and theoretical investigations on the polarizabilities of the nucleon is presented. This includes a confirmation of the validity of the previously introduced recommended values of the polarizabilities [1,2]. It is shown that the only meaningful approach to a prediction of the polarizabilities is obtained from the nonsubtracted dispersion theory, where the appropriate degrees of freedom taken from other precise experimental data are taken in account. The present values of the recommended polarizabilities are $α_p= 12.0 \pm 0.5$, $β_p= 1.9 \mp 0.5$, $α_n= 12.6 \pm 1.2$, $β_n= 2.6 \mp 1.2$ in units of $10^{-4}$fm$^3$ and $γ^{(p)}_π= -36.4 \pm 1.5$, $γ^{(n)}_π=+58.6 \pm 4.0$, $γ^{(p)}_0=-0.58 \pm 0.20$, $γ^{(n)}_0= +0.38\pm 0.22$ in units of $10^{-4}$fm$^4$.

hep-ph↗

arXiv2019

Netboost: Boosting-supported network analysis improves high-dimensional omics prediction in acute myeloid leukemia and Huntington's disease

Background: State-of-the art selection methods fail to identify weak but cumulative effects of features found in many high-dimensional omics datasets. Nevertheless, these features play an important role in certain diseases. Results: We present Netboost, a three-step dimension reduction technique. First, a boosting-based filter is combined with the topological overlap measure to identify the essential edges of the network. Second, sparse hierarchical clustering is applied on the selected edges to identify modules and finally module information is aggregated by the first principal components. The primary analysis is than carried out on these summary measures instead of the original data. We demonstrate the application of the newly developed Netboost in combination with CoxBoost for survival prediction of DNA methylation and gene expression data from 180 acute myeloid leukemia (AML) patients and show, based on cross-validated prediction error curve estimates, its prediction superiority over variable selection on the full dataset as well as over an alternative clustering approach. The identified signature related to chromatin modifying enzymes was replicated in an independent dataset of AML patients in the phase II AMLSG 12-09 study. In a second application we combine Netboost with Random Forest classification and improve the disease classification error in RNA-sequencing data of Huntington's disease mice. Conclusion: Netboost improves definition of predictive variables for survival analysis and classification. It is a freely available Bioconductor R package for dimension reduction and hypothesis generation in high-dimensional omics applications.

q-bio.GN↗

arXiv2019

Mass and structure of the nucleon: Gluon trace anomaly versus spontaneous symmetry breaking

Two different approaches to mass and structure of the nucleon are discussed in recent works, ${\it viz.}$ (case 1) the QCD lagrangian evaluated via lattice calculations and (case ii) spontaneous symmetry breaking mediated by the $σ$ field. These approaches are complementary in the sense that the QCD lagrangian makes use of the gluon content of the nucleon entering in terms of the gluon trace-anomaly and ignores the effects of $q{\bar q}$ vacuum polarization, whereas in spontaneous symmetry breaking masses are formed by attaching $q{\bar q}$ pairs to the valence quarks, thus giving them a definite mass which is named the constituent mass. By the same process the $q{\bar q}$ pairs of the vacuum polarization acquire mass and in this form are the elements of the quark condensate, having an up-quark and a down-quark component. A linear combination of these two components in the form $σ=1/\sqrt{2}(u{\bar u} + d{\bar d})$ shows up as the $σ$ field. It is shown that (case i) corresponds to an unstable nucleon configuration whereas (case ii) corresponds to a stable nucleon configuration as observed in low-energy photo-nuclear and pion-nuclear reactions.

hep-ph↗

arXiv2019

The population-attributable fraction for time-dependent exposures and competing risks - A discussion on estimands

The population-attributable fraction (PAF) quantifies the public health impact of a harmful exposure. Despite being a measure of significant importance an estimand accommodating complicated time-to-event data is not clearly defined. We discuss current estimands of the PAF used to quantify the public health impact of an internal time-dependent exposure for data subject to competing outcomes. To overcome some limitations, we proposed a novel estimand which is based on dynamic prediction by landmarking. In a profound simulation study, we discuss interpretation and performance of the various estimands and their estimators. The methods are applied to a large French database to estimate the health impact of ventilator-associated pneumonia for patients in intensive care.

stat.AP↗

arXiv2019

The population-attributable fraction for time-dependent exposures using dynamic prediction and landmarking

The public health impact of a harmful exposure can be quantified by the population-attributable fraction (PAF). The PAF describes the attributable risk due to an exposure and is often interpreted as the proportion of preventable cases if the exposure could be extinct. Difficulties in the definition and interpretation of the PAF arise when the exposure of interest depends on time. Then, the definition of exposed and unexposed individuals is not straightforward. We propose dynamic prediction and landmarking to define and estimate a PAF in this data situation. Two estimands are discussed which are based on two hypothetical interventions that could prevent the exposure in different ways. Considering the first estimand, at each landmark the estimation problem is reduced to a time-independent setting. Then, estimation is simply performed by using a generalized-linear model accounting for the current exposure state and further (time-varying) covariates. The second estimand is based on counterfactual outcomes, estimation can be performed using pseudo-values or inverse-probability weights. The approach is explored in a simulation study and applied on two data examples. First, we study a large French database of intensive care unit patients to estimate the population-benefit of a pathogen-specific intervention that could prevent ventilator-associated pneumonia caused by the pathogen Pseudomonas aeruginosa. Moreover, we quantify the population-attributable burden of locoregional and distant recurrence in breast cancer patients.

stat.AP↗

arXiv2019

Causal inference with multi-state models - estimands and estimators of the population-attributable fraction

The population-attributable fraction (PAF) is a popular epidemiological measure for the burden of a harmful exposure within a population. It is often interpreted causally as proportion of preventable cases after an elimination of exposure. Originally, the PAF has been defined for cohort studies of fixed length with a baseline exposure or cross-sectional studies. An extension of the definition to complex time-to-event data is not straightforward. We revise the proposed approaches in literature and provide a clear concept of the PAF for these data situations. The conceptualization is achieved by a proper differentiation between estimands and estimators as well as causal effect measures and measures of association.

stat.ME↗

arXiv2018

Game time: statistical contests in the classroom

We describe a contest in variable selection which was part of a statistics course for graduate students. In particular, the possibility to create a contest themselves offered an additional challenge for more advanced students. Since working with data is becoming more important in teaching statistics, we greatly encourage other instructors to try the same.

stat.OT↗

arXiv2016

A flexible multivariate random effects proportional odds model with application to adverse effects during radiation therapy

Radiation therapy in patients with head and neck cancer has a toxic effect on mucosa, the soft tissue in and around the mouth. Hence mucositis is a serious common side effect and is a condition characterized by pain and inflammation of the surface of the mucosa. Although the mucosa recovers during breaks of and following the radiotherapy course the recovery will depend on the type of tissue involved and on its location. We present a novel flexible multivariate random effects proportional odds model which takes account of the longitudinal course of oral mucositis at different mouth sites and of the radiation dosage (in terms of cumulative dose). The model is an extension of the {\em proportional odds model} which is used for ordinal response variables. Our model includes the ordinal multivariate response of the mucositis score by location, random intercepts for individuals and includes a non-linear function of cumulative radiation dose. The model allows to test whether sensitivity differs by mouth sites after having adjusted for site specific cumulative radiation dose. The model also allows to check whether and how the (non-linear) effect of site specific dose differs by site. We fit the model to longitudinal patient data from a prospective observation and find that after adjusting for cumulative dose, upper, lower lips and mouth floor are associated with the lowest mucositis scores and hard and soft palate are associated with the highest mucositis scores. This implies the possibility that tissues at different mouth locations differ in their sensitivity to the toxic effect of radiation. We also find that cumulative dose followed by mouth site are the strongest predictors of mucositis, and the effects of age and gender are negligible.

stat.AP↗

arXiv2015

Mass generation via the Higgs boson and the quark condensate of the QCD vacuum

The Higgs boson, recently discovered with a mass of 125.09$\pm$0.24 GeV is known to mediate the masses of elementary particles, but only 2% of the mass of the nucleon. Extending a previous investigation [1] and including the strange-quark sector, hadron masses are derived from the quark condensate of the QCD vacuum and from the effects of the Higgs boson. These calculations include the $π$ meson, the nucleon and the scalar mesons $σ(600)$, $κ(800)$, $a_0(980)$ $f_0(980)$ and $f_0(1370)$. The predicted second $σ$ meson $σ'(1344)=|s\bar{s}\rangle$, is investigated and identified with the $f_0(1370)$ meson. An outlook is given on the hyperons $Λ$, $Σ^{0,\pm}$ and $Ξ^{0,-}$.

hep-ph↗

arXiv2014

Nambu's Nobel Prize, the $σ$ meson and the mass of visible matter

The electroweak Higgs boson has been discovered in ongoing experiments at the LHC, leading to a mass of this particle of 126 GeV. This Higgs boson mediates the generation of mass for elementary particles, including the mass of elementary (current) quarks. These current-quark masses leave 98% of the mass of the atom unexplained. This large fraction is mediated by strong interaction, where instead of the Higgs boson the $σ$ meson is the mediating particle. Though already discovered in 1957 by Schwinger, the $σ$ meson has been integrated out in many theories of hadron properties because it had not been observed and was doubted to exist. With the observation of the $σ$ meson in recent experiments on Compton scattering by the nucleon at MAMI (Mainz) it has become timely to review the status of experimental and theoretical researches on this topic.

hep-ph↗

arXiv2014

Dispersion theory of nucleon polarizabilities and outlook on chiral effective field theory

Based on Compton scattering and meson photoproduction data the polarizabilities of the nucleon are precisely studied and well understood due to recent experimental and theoretical work based on nonsubtracted dispersion relations. The {\it recommended} experimental values are $α_p=12.0\pm 0.6$, $(12.0)$, $β_p=1.9\mp 0.6$, $(1.9)$, $α_n=12.5\pm 1.7$, $(12.7\pm 0.9)$, $β_n=2.7\mp 1.8$, $(2.5\mp 0.9)$ in units of $10^{-4}$fm$^3$ and $γ^{(p)}_π=-36.4\pm 1.5$, $(-36.6)$, $γ^{(n)}_π=+58.6\pm 4.0$, $(58.3)$, $(γ^{(p)}_0=-0.58\pm 0.20)$, $γ^{(n)}_0=0.38\pm 0.22)$ in units of $10^{-4}$fm$^4$ [1]. The numbers given in parentheses are predicted values. It is shown that all versions of chiral effective field theories applied in analyses of nucleon polarizabilities and Compton scattering ignore essential effects of $ω$, $ρ$ and $σ$ exchanges and of pseudoscalar $π$N coupling.

hep-ph↗

arXiv2013

Dispersion theory of nucleon Compton scattering and polarizabilities

A status report on the topic Compton scattering and polarizabilities is presented with emphasis on the scalar t-channel as entering into dispersion theory. Precise values for the polarizabilities are obtained leading to $α_p = 12.0\pm 0.6$ $(12.0)$, $β_p=1.9\mp 0.6$ $(1.9)$, $α_n= 12.5\pm 1.7$ $(13.4)$, $β_n= 2.7 \mp 1.8$ $(1.8)$ in units of $10^{-4}$ fm$^3$ and $γ^{(p)}_π= -36.4 \pm 1.5$ $(-36.6)$, $γ^{(n)}_π= 58.6 \pm 4.0$ $(58.3)$, $(γ^{(p)}_0= -0.58\pm 0.20)$, $(γ^{(n)}_0 = +0.38\pm 0.22)$ in units of $10^{-4}$ fm$^4$, for the proton (p) and neutron (n), respectively. The data given with an error are {\it recommended} experimental values with updates compared to [1] where necessary, the data in parentheses are predicted values. These predicted values are not contained in [1], but are the result of a newly developed analysis which is the main topic of the present paper. The most important recent discovery is that the largest part of the electric polarizability and the total diamagnetic polarizability of the nucleon are properties of the $σ$ meson as part of the constituent-quark structure, as expected from the mechanism of chiral symmetry breaking. This view is supported by an experiment on Compton scattering by the proton carried out in the second resonance region, where a large contribution from the $σ$ meson enters into the scattering amplitudes. This experiment led to a determination of the mass of the $σ$ meson of $m_σ= 600 \pm 70$ MeV. From the experimental $α_p$ and predicted differences $(α_n - α_p)$ neutron polarizabilities in the range $α_n= 12.0 - 13.4$ are predicted, where the uncertainties are related to the $f_0(980)$ and $a_0(980)$ scalar mesons.

hep-ph↗

arXiv2011

Conference Report: Structure of scalar mesons and the Higgs sector of strong interaction

The $σ$ mesons may be considered as the Higgs boson of strong interaction. While the observation of the electroweak Higgs boson is the primary goal in ongoing experiments at the LHC, the $σ$ meson is by now well studied both as an on-shell particle and as a virtual particle while being part of the constituent quark. This makes it timely to give an overview of the present status of the Higgs sector of strong interaction which includes the scalar mesons $σ(600)$, $κ(800)$, $f_0(980)$ and $a_0(980)$ together with the pseudo Goldstone bosons $π$, $K$ and $η$.

hep-ph↗

arXiv2011

Structure of scalar mesons and the Higgs sector of strong interaction

The scalar mesons $σ(600)$, $κ(800)$, $f_0(980)$ and $a_0(980)$ together with the pseudo Goldstone bosons $π$, $K$, and $η$ may be considered as the Higgs sector of strong interaction. After a long time of uncertainty about the internal structure of the scalar mesons there now seems to be consistency which is in line with the major parts of experimental observations. Great progress has been made by introducing the unified model of Close and Törnqvist. This model states that mesons below 1 GeV may be understood as $q^2\bar{q}^2$ in S-wave with some $q\bar{q}$ in P-wave in the center, further out they rearrange as $(q\bar{q})^2$ and finally as meson-meson states. The P-wave component inherent in the structure of the neutral scalar mesons can be understood as a doorway state for the formation of the scalar meson via two-photon fusion, whereas in nucleon Compton scattering these P-wave components serve as intermediate states. The masses of the scalar mesons are predicted in terms of spontaneous and explicit symmetry breaking.

hep-ph↗

arXiv2011

Structure of the nucleon and spin-polarizabilities

Spin-polarizabilities are predicted by calculating the cross-section difference $σ_{3/2}-σ_{1/2}$ from available data for the resonance couplings $A_{3/2}$ and $A_{1/2}$ and CGLN amplitudes. The forward spin-polarizabilities are predicted to be $γ^{(p)}_0=-0.58\pm 0.20$ and $γ^{(n)}_0=+0.38\pm 0.22$ in units of $10^{-4}$fm$^4$ where the different signs are found to be due to the isospin dependencies of the $E_{0+}$ and the $(M,E)^{(1/2)}_{1+}$ amplitudes. The backward spin-polarizabilities are predicted to be $γ^{(p)}_π=-36.6$ and $γ^{(n)}_π=+58.3$, to be compared with the experimental values $γ^{(p)}=-36.4\pm 1.5$ and $γ^{(n)}_π=+58.6\pm 4.0$. Electric $γ_E$ and magnetic $γ_M$ spin-polarizabilities are introduced and discussed in terms of the $E1$ and $M1/E2$ components of the photo-absorption cross section of the nucleon.

hep-ph↗

arXiv2010

A coordinate-wise optimization algorithm for the Fused Lasso

L1 -penalized regression methods such as the Lasso (Tibshirani 1996) that achieve both variable selection and shrinkage have been very popular. An extension of this method is the Fused Lasso (Tibshirani and Wang 2007), which allows for the incorporation of external information into the model. In this article, we develop new and fast algorithms for solving the Fused Lasso which are based on coordinate-wise optimization. This class of algorithms has recently been applied very successfully to solve L1 -penalized problems very quickly (Friedman et al. 2007). As a straightforward coordinate-wise procedure does not converge to the global optimum in general, we adapt it in two ways, using maximum-flow algorithms and a Huber penalty based approximation to the loss function. In a simulation study, we evaluate the speed of these algorithms and compare them to other standard methods. As the Huber-penalty based method is only approximate, we also evaluate its accuracy. Apart from this, we also extend the Fused Lasso to logistic as well as proportional hazards models and allow for a more flexible penalty structure.

stat.CO↗

arXiv2010

Observation of the Higgs Boson of strong interaction via Compton scattering by the nucleon

It is shown that the Quark-Level Linear $σ$ Model (QLL$σ$M) leads to a prediction for the diamagnetic term of the polarizabilities of the nucleon which is in excellent agreement with the experimental data. The bare mass of the $σ$ meson is predicted to be $m_σ=666$ MeV and the two-photon width $Γ(σ\toγγ)=(2.6\pm 0.3)$ keV. It is argued that the mass predicted by the QLL$σ$M corresponds to the $γγ\toσ\to NN$ reaction, i.e. to a $t$-channel pole of the $γN\to Nγ$ reaction. Large -angle Compton scattering experiments revealing effects of the $σ$ meson in the differential cross section are discussed. Arguments are presented that these findings may be understood as an observation of the Higgs boson of strong interaction while being part of the constituent quark.

hep-ph↗