bluuebunny/crossref_metadata_2025_split huggingface dataset:
A general, prediction error‐based criterion for selecting model complexity for high‐dimensional survival models
Authors: Porzelius Christine , Schumacher Martin , Binder Harald 
Published: March 2010

AbstractWhen fitting predictive survival models to high‐dimensional data, an adequate criterion for selecting model complexity is needed to avoid overfitting. The complexity parameter is typically selected by the predictive partial log‐likelihood (PLL) estimated via cross‐validation. As an alternative criterion, we propose a relative version of the integrated prediction error curve (IPEC), which can be stably estimated via bootstrap resampling. The IPEC has the advantage of being applicable for models and fitting techniques where the PLL is not available. To investigate the performance of this new criterion, a simulation study is carried out, mimicking microarray survival data. Additionally, model selection by predictive PLL, estimated via bootstrap resampling instead of cross‐validation, is examined. It is seen that this mostly results in similar prediction performance of the selected models, compared to estimates based on cross‐validation. Model selection by bootstrap estimates of the IPEC performs about as well as selection by cross‐validation estimates of the PLL. Therefore, it is expected to be a reasonable alternative in cases where there is no PLL. Similar results are seen in the analysis of a microarray survival data set from patients with diffuse large‐B‐cell lymphoma. Copyright © 2010 John Wiley & Sons, Ltd.
Proportional subdistribution hazards modeling offers a summary analysis, even if misspecified
Authors: Grambauer Nadine , Schumacher Martin , Beyersmann Jan 
Published: March 2010

AbstractCompeting risks model time‐to‐first‐event and the event type. Our motivating data example is the ONKO‐KISS study on the occurrence of infections in neutropenic patients after stem‐cell transplantation with first‐event‐types ‘infection’ and ‘end of neutropenia’. The standard approach to study the effects of covariates in competing risks is to assume each event‐specific hazard (ESH) to follow a proportional hazards model. However, a summarizing probability interpretation of the different event‐specific effects of one covariate can be challenging. This difficulty has led to the development of the proportional subdistribution hazards model of a competing event of interest. However, one model specification usually precludes the other. Assuming proportional ESHs, we find that the subdistribution log‐hazard ratio may show a pronounced time‐dependency, even changing sign. Still, the subdistribution analysis is useful by estimating the least false parameter (LFP), a time‐averaged effect on the cumulative event probabilities. In examples, we find that the LFP offers a robust summary of the effects on the ESHs for different observation periods, ranging from heavy censoring to no censoring at all. In particular, if there is no effect on the competing ESH, the subdistribution log‐hazard ratio is close to the event‐specific log‐hazard ratio of interest. We reanalyze an interpretationally challenging example from the ONKO‐KISS study and conduct a simulation study, where we find that the LFP is reliably estimated by the subdistribution analysis even for moderate sample sizes. Copyright © 2010 John Wiley & Sons, Ltd.
Estimating adjusted risk difference (RD) and number needed to treat (NNT) measures in the Cox regression model
Authors: Laubender R. P. , Bender R. 
Published: March 2010

AbstractIn medical research, risk difference (RD) and number needed to treat (NNT) measures for survival times have been mainly proposed without consideration of covariates. In this paper, we develop adjusted RD and NNT measures for use in observational studies with survival time outcomes within the framework of the Cox proportional hazards regression model taking the distribution of confounders into account. We consider the typical situation of a cohort study in which the effect of an exposure on a survival time outcome is investigated and important covariates have to be taken into account. The exposure effect described by means of the RD and NNT measures in dependence on whether the effect of allocating an exposure to unexposed persons (number needed to be exposed) or that of removing an exposure from exposed persons (exposure impact number) is considered. Estimation of these adjusted RD and NNT measures is performed by using the average RD approach recently developed for logistic regression. To determine standard errors and confidence intervals for these estimators we use two approaches, the delta method with respect to the regression coefficients of the Cox model and bootstrapping and compare each other. The performance of these estimators is assessed by performing Monte Carlo simulations demonstrating clear advantages of the bootstrap method. The proposed method for point and interval estimation of adjusted RD and NNT measures in the Cox model is illustrated by means of data of the Düsseldorf Obesity Mortality Study (DOMS). Copyright © 2010 John Wiley & Sons, Ltd.
Bias‐reduced and separation‐proof conditional logistic regression with small or sparse data sets
Authors: Heinze Georg , Puhr Rainer 
Published: March 2010

AbstractConditional logistic regression is used for the analysis of binary outcomes when subjects are stratified into several subsets, e.g. matched pairs or blocks. Log odds ratio estimates are usually found by maximizing the conditional likelihood. This approach eliminates all strata‐specific parameters by conditioning on the number of events within each stratum. However, in the analyses of both an animal experiment and a lung cancer case–control study, conditional maximum likelihood (CML) resulted in infinite odds ratio estimates and monotone likelihood. Estimation can be improved by using Cytel Inc.'s well‐known LogXact software, which provides a median unbiased estimate and exact or mid‐pconfidence intervals. Here, we suggest and outline point and interval estimation based on maximization of a penalized conditional likelihood in the spirit of Firth's (Biometrika1993; 80:27–38) bias correction method (CFL). We present comparative analyses of both studies, demonstrating some advantages of CFL over competitors. We report on a small‐sample simulation study where CFL log odds ratio estimates were almost unbiased, whereas LogXact estimates showed some bias and CML estimates exhibited serious bias. Confidence intervals and tests based on the penalized conditional likelihood had close‐to‐nominal coverage rates and yielded highest power among all methods compared, respectively. Therefore, we propose CFL as an attractive solution to the stratified analysis of binary data, irrespective of the occurrence of monotone likelihood. A SAS program implementing CFL is available at:http://www.muw.ac.at/msi/biometrie/programs. Copyright © 2010 John Wiley & Sons, Ltd.
Practical considerations for optimal designs in clinical dose finding studies
Authors: Bretz Frank , Dette Holger , Pinheiro Jose C. 
Published: March 2010

AbstractA key objective in the clinical development of a medicinal drug is the determination of an adequate dose level and, more broadly, the characterization of its dose response relationship. If the dose is set too high, safety and tolerability problems are likely to result, while selecting too low a dose makes it difficult to establish adequate efficacy in the confirmatory phase, possibly leading to a failed program. Hence, dose finding studies are of critical importance in drug development and need to be planned carefully. In this paper, we focus on practical considerations for establishing efficient study designs to estimate relevant target doses. We consider optimal designs for estimating both the minimum effective dose and the dose achieving a certain percentage of the maximum treatment effect. These designs are compared with D‐optimal designs for a given dose response model. Extensions to robust designs accounting for model uncertainty are also discussed. A case study is used to motivate and illustrate the methods from this paper. Copyright © 2010 John Wiley & Sons, Ltd.
Bootstrap‐based methods for estimating standard errors in Cox's regression analyses of clustered event times
Authors: Xiao Yongling , Abrahamowicz Michal 
Published: March 2010

AbstractWe propose two bootstrap‐based methods to correct the standard errors (SEs) from Cox's model for within‐cluster correlation of right‐censored event times. The cluster‐bootstrap method resamples, with replacement, only the clusters, whereas the two‐step bootstrap method resamples (i) the clusters, and (ii) individuals within each selected cluster, with replacement. In simulations, we evaluate both methods and compare them with the existing robust variance estimator and the shared gamma frailty model, which are available in statistical software packages. We simulate clustered event time data, with latent cluster‐level random effects, which are ignored in the conventional Cox's model. For cluster‐level covariates, both proposed bootstrap methods yield accurate SEs, and type I error rates, and acceptable coverage rates, regardless of the true random effects distribution, and avoid serious variance under‐estimation by conventional Cox‐based standard errors. However, the two‐step bootstrap method over‐estimates the variance for individual‐level covariates. We also apply the proposed bootstrap methods to obtain confidence bands around flexible estimates of time‐dependent effects in a real‐life analysis of cluster event times. Copyright © 2010 John Wiley & Sons, Ltd.
Estimators and confidence intervals for the marginal odds ratio using logistic regression and propensity score stratification
Authors: Stampf Susanne , Graf Erika , Schmoor Claudia , Schumacher Martin 
Published: March 2010

AbstractPropensity score methods are widely used to estimate treatment or exposure effects in observational studies. In studies with binary response the effect can be described as an odds ratio, and the Mantel–Haenszel estimator is traditionally used for stratified data. Although propensity score methods are designed for marginal treatment effects, it has been shown that the Mantel–Haenszel estimator stratified for propensity score is a questionable estimator for the marginal odds ratio, which describes the change in odds of response if everybody versus nobody were treated.We studied recently proposed alternative estimators for the marginal odds ratio, one stratified for propensity score, the other derived from logistic regression. Additionally, we adapted the methodology of the logistic regression based estimator for the derivation of a marginal odds ratio estimator to covariate adjustment by the propensity score. We also derived corresponding variance estimators using the Delta‐method.The estimators were illustrated and compared to the inverse probability weighted estimator and the stratified Mantel–Haenszel estimator in a study dealing with respiratory tract infections in children in Germany. Furthermore, simulation studies that were carried out to investigate relative bias, variance and coverage probability showed reasonable performance of marginal odds ratio estimators if response rates or regression based approaches were used. Their variances were accurately estimated. In contrast, the stratified Mantel–Haenszel estimator was substantially biased in some situations due to problems of non‐collapsibility and thus it is generally inappropriate for a reliable estimation of the marginal odds ratio. Copyright © 2010 John Wiley & Sons, Ltd.
The hidden costs of outsourcing: evidence from patent data
Authors: Reitzig Markus , Wagner Stefan 
Published: March 2010

AbstractDrawing on patent data for approximately 500 firms over 20 years, we advance recent theory on firm boundaries and test these propositions for the first time. We first provide evidence for the existence of knowledge complementarities between vertically related activities in a firm's value chain by showing that firms face increasing (decreasing) performance in conducting downstream activities (i.e., patent litigation) the less (more) they outsource related upstream activities (i.e., patent filing). We then propose and empirically demonstrate that vertical integration benefits through learning differ from vertical outsourcing costs through forgetting. We show that firms can partly offset these hidden outsourcing costs by sourcing similar upstream products from internal and external suppliers. Copyright © 2010 John Wiley & Sons, Ltd.
Two steel bridges for the high speed railway line in Spain
Authors: Sobrino Juan A. 
Published: March 2010

AbstractThis article synthesises the design criteria and erection process of two steel bridges designed for the high speed rail line connecting Madrid, Barcelona and the French Border. Both structures cross over existing infrastructures, near Barcelona, with a limited vertical clearance in order to reduce environmental impact. The conceptual design is similar for the two structures: a composite steel‐concrete deck suspended on steel tied curved members. An innovative solution, at least for the Spanish HSR lines, that has been used in the past in concrete road bridges. These bridges are two of the three first steel structures built for the HSR in Spain.Llinars Bridge crosses, at a very high skew angle, one of the busiest highways (AP‐7) in Spain. This viaduct has an overall length of 574 m with a maximum span of 75 m. Sant Boi Bridge crosses several existing infrastructures (highway, road and railway). The length of the bridge is 870 m with a maximum span of 63 m.Zwei Stahlbrücken für die Hochgeschwindigkeitsstrecke der Eisenbahn in Spanien. Dieser Beitrag beschreibt die Entwurfskriterien und den Bauprozess von zwei stählernen Eisenbahnbrücken auf der Hochgeschwindigkeitsstrecke Madrid, Barcelona bis zur französischen Grenze. Beide Bauwerke in der Nähe von Barcelona überspannen bestehende Infrastrukturen mit einer minimalen Bauhöhe, um den Eingriff in die Umgebung so weit wie möglich zu reduzieren. Der konzeptuelle Entwurf ist bei beiden Brücken ähnlich: Eine Stahlverbund‐Fahrbahn wird durch gekrümmte Stahlzugglieder unterstützt. Dies ist für die spanischen Hochgeschwindigkeits‐Eisenbahnbrücken eine innovative Lösung, denn in der Vergangenheit wurden ausschließlich Betonbrücken genutzt. Die Brücken sind zwei der ersten drei stählernen Tragwerke, die für die spanische Hochgeschwindigkeitsbahn gebaut wurden.Die Llinars‐Brücke überspannt in einem sehr spitzen Winkel eine der meistbefahrenen Autobahnen (AP‐7) von Spanien. Die Brücke hat eine Gesamtlänge von 574 m mit einer maximalen Stützweite von 75 m. Die Sant Boi Brücke kreuzt mehrere bestehende Infrastrukturanlagen (Autobahn, Straße und Eisenbahn). Die Gesamtlänge beträgt 870 m, die maximale Stützweite 63 m.
Lobby Fassade und Vordächer für den Trump Tower, Chicago
Authors: Wellershoff Frank , Utz Sebastian , Balint Ladislaus 
Published: March 2010

AbstractDer Donald Trump Tower inmitten Chicagos beherbergt in seinen 92 Stockwerken neben 339 5‐Sterne Hotelzimmern 486 Luxusappartements und Wohnungen (Bild 1). Mit seinen 427 m Höhe rangiert das Gebäude derzeit auf Rang 7 der höchsten Gebäude der Welt (Quelle CTBUH). Besonders im Eingangsbereich wurden höchste Ansprüche an die Transparenz der Fassade und die Oberflächenqualität der verwendeten Materialien Glas und Edelstahl gelegt. Nur durch aufwendige Bemessungen, begleitet durch Bauteilversuche und umfangreiche Bemusterungen der Bauteile, konnte das außerordentliche Niveau dieses Gebäudes realisiert werden.Lobby façade and canopy for the Trump Tower, Chicago. The Trump International Hotel and Tower located in the heart of Downtown Chicago offers 339 five‐star hotel rooms and 486 luxury condominium residences (fig. 1). At 92 stories and a height of 427 m to the top of the spire, The Trump Tower is now the 7th tallest building of the world (CTBUH ranking). Highest quality concerning the façade transparency and the quality of the materials and surfaces was requested especially at the entrance area. Extensive calculations and prototype testing as well as lots of visual samples were required to meet the highest demands for this extraordinary building.
Profilbauglas – Prüfmethodik, Tragverhalten und Produktentwicklung
Authors: Kasper Ruth , Langosch Katharina , Feldmann Markus , Sedlacek Gerhard , Tabone Salvatore 
Published: March 2010

AbstractWährend technisch gekühlte Profilbaugläser bereits seit über 40 Jahren zur Verkleidung von Zweck‐ oder Industriebauten verwendet werden, sind thermisch vorgespannte Profilbaugläser im Glasbau relativ neu und wecken vermehrt das Interesse der Architekten. Das sich durch höhere Festigkeit und feinkrümeliges Bruchbild auszeichnende thermisch vorgespannte Profilbauglas eröffnet Einsatzgebiete, die bisher Einscheibensicherheitsgläsern vorbehalten waren. Der vorliegende Artikel beschreibt die Einbaumöglichkeiten von Profilbauglas, die verwendete Prüfmethodik und das zugehörige Bemessungskonzept.Channel shaped glass – Testing method, structural behaviour and product development. Before, channel shaped glass was used as a cost efficient material for the cladding of industrial buildings. Recently, architecture discovered channel shaped glass as a design element. Newly, the glass industry offers channel shaped glass as thermally toughened glass and the material is able to respect and to fulfil security aspects compared to fully thermally toughened flat glass. The paper describes the application of channel shaped glass, the test procedure und the design concept.
Gekrümmte Glasflächen – Zusammenspiel von Geometrie und Glasdetaillierung
Authors: Laufs Wilfried , Vilkner Gregor 
Published: March 2010

AbstractDer folgende Aufsatz aus dem Bereich der Fassadenplanung beschreibt, welche Möglichkeiten sich für die Glaseindeckung gekrümmter Gebäudehüllen ergeben. Insbesondere viereckige Isolierglasscheiben bieten dazu Vorteile aus Sicht der Bauphysik und der Baukosten. Für Trockenfugen sollten Flachglaselemente auch nach Einbau vollständig eben gehalten werden, um Gebrauchstauglichkeit der Primärversiegelung sicherzustellen, während für nassversiegelte Glasfugen eine gewisse Glasverwindung durchaus möglich ist, sofern Detaillierung und 3D‐Geometrie sinnvoll zusammenspielen. Wird die Glasverwindung (“twist”) zu groß, kann eine geschuppte Stufenverglasung angestrebt werden. In allen Fällen bieten der Ansatz von Building Information Modeling (BIM) und digitaler Fabrikation wesentliche Vorteile für Planung und Realisierung solcher komplexer verglaster Oberflächen.Clad curved building surfaces – Interaction of geometry and glass detailing. The following article addresses the field of façade engineering, describing different options how to clad curved building surfaces. Especially insulated glazing unit quadrangles offer advantages related to building physics and cost. For dry joints, flat glazing units should remain flat also after installation, to achieve long‐term serviceability of the primary edge spacer seal, while for wet joints a certain amount of glazing twist is well possible to panelise curved surfaces, given that their detailing and 3D geometry set‐up work well together. If the glazing twist exceeds certain limits, a scaled and stepped glazing facade can be aimed for. In all cases the Building Information Modeling (BIM) and digital fabrication approach offer substantial advantages for the planning and realisation process of such complex curved building skin surfaces.
Using orthogonal pairs of rollers on concave beds (OPRCB) as a base isolation system—part I: analytical, experimental and numerical studies of OPRCB isolators
Authors: Hosseini Mahmood , Soroor Amirhossein 
Published: March 2010

SUMMARYA somehow new isolating system is introduced for short‐ to mid‐rise buildings. It does not need high technology for manufacturing and is not costly, contrary to other existing systems like lead‐rubber bearing or friction pendulum bearing systems. Each isolator of the proposed system consists of two Orthogonal Pairs of Rollers on Concave Beds (OPRCB). Rolling rods installed in two orthogonal directions make possible the movement of the superstructure in all horizontal directions. The concave beds, in addition to giving the system both restoring and re‐centring capabilities, make the force–displacement behaviour of the isolators to be of hardening type. The results of the studies on the specifications of the proposed isolating system and its application to buildings can be presented in two parts. Part I relates to the analytical formulations and the results of experimental and numerical studies of the system's mechanical feature, including its dynamical properties, and part II focuses on the effectiveness of the proposed isolation system in seismic response reduction of low‐ to mid‐rise buildings. In part I of the work, presented in this paper, at first general features of the OPRCB isolator are explained and the analytical formulation, governing its dynamic motion, is derived and discussed in detail. Then, the results of experimental and numerical investigations, including the lateral load displacement relationship of the OPRCB isolators under various vertical loads, obtained by both Finite Element Analyses (FEA) and laboratory tests are presented (FEA results have been verified by the laboratory tests). Finally, responses of some Single Degree of Freedom (SDOF) systems, isolated by OPRCB devices, subjected to simultaneous effect of horizontal and vertical ground motions, are presented and compared with responses of their fixed‐base counterparts. Based on the numerical calculations, it is observed that the oscillation period of the isolated SDOF system is independent of its mass, the initial amplitude of its free vibration response and the value of rolling resistance coefficient. With regard to seismic response reduction it is seen that the amount of absolute accelerations in the SDOF systems, isolated by OPRCB devices, can be reduced drastically in comparison with the fixed‐base systems. Results also show that if the rollers and cylindrical beds are made of high‐strength steel materials, the system can be used effectively under the vertical loads of about the axial forces of ground floor columns in ordinary buildings up to 14 storeys. Copyright © 2010 John Wiley & Sons, Ltd.
A method for design of seismic resistant structures with viscoelastic dampers
Authors: Ribakov Y. , Agranovich G. 
Published: March 2010

AbstractViscoelastic (VE) dampers are widely used for enhancing structural response to earthquakes, wind and other dynamic loadings. Various methods were proposed for effective design of passive control systems with VE dampers. These methods are based on desired level of additional damping, eigenvalue assignment, modal strain energy, linear quadratic regulator control theories and other approaches. This paper presents an alternative method based on an optimal active control algorithm. At the first stage for design purposes, the structure is assumed to be an active controlled one. The active control is designed, based on a modified LQR optimization method previously developed by the authors. By analyzing the response of the structure to an artificial white noise earthquake, force‐displacement relationship in the active devices is obtained. A structure with VE dampers in an ideal case should have a response that is as close as possible to that of the active controlled structure. The properties of VE dampers are obtained assuming that additional stiffness and energy dissipated in active and VE dampers at the peak inter‐storey displacement are equal. Numerical analysis of an eight‐storey structure was carried out. Natural earthquake records were used to verify the efficiency of the proposed method. It was demonstrated that seismic response in a structure with VE dampers, designed according to the proposed method, is similar to that with active controlled devices. Copyright © 2010 John Wiley & Sons, Ltd.