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Biometrical Journal. Biometrische Zeitschrift

Montserrat Rué, Eleni-Rosalina Andrinopoulou, Danilo Alvares, Carmen Armero, Anabel Forte, Lluis Blanch
Mechanical ventilation is a common procedure of life support in intensive care. Patient-ventilator asynchronies (PVAs) occur when the timing of the ventilator cycle is not simultaneous with the timing of the patient respiratory cycle. The association between severity markers and the events death or alive discharge has been acknowledged before, however, little is known about the addition of PVAs data to the analyses. We used an index of asynchronies (AI) to measure PVAs and the SOFA (sequential organ failure assessment) score to assess overall severity...
August 11, 2017: Biometrical Journal. Biometrische Zeitschrift
Meike Köhler, Nikolaus Umlauf, Andreas Beyerlein, Christiane Winkler, Anette-Gabriele Ziegler, Sonja Greven
The joint modeling of longitudinal and time-to-event data is an important tool of growing popularity to gain insights into the association between a biomarker and an event process. We develop a general framework of flexible additive joint models that allows the specification of a variety of effects, such as smooth nonlinear, time-varying and random effects, in the longitudinal and survival parts of the models. Our extensions are motivated by the investigation of the relationship between fluctuating disease-specific markers, in this case autoantibodies, and the progression to the autoimmune disease type 1 diabetes...
August 10, 2017: Biometrical Journal. Biometrische Zeitschrift
Dimitris Rizopoulos, Geert Molenberghs, Emmanuel M E H Lesaffre
A key question in clinical practice is accurate prediction of patient prognosis. To this end, nowadays, physicians have at their disposal a variety of tests and biomarkers to aid them in optimizing medical care. These tests are often performed on a regular basis in order to closely follow the progression of the disease. In this setting, it is of interest to optimally utilize the recorded information and provide medically relevant summary measures, such as survival probabilities, which will aid in decision making...
August 9, 2017: Biometrical Journal. Biometrische Zeitschrift
Gregory Haber, Yaakov Malinovsky
Group testing estimation, which utilizes pooled rather than individual units for testing, has been an ongoing area of research for over six decades. While it is often argued that such methods can yield large savings in terms of resources and/or time, these benefits depend very much on the initial choice of pool sizes. In fact, when poor group sizes are used, the results can be much worse than those obtained using standard techniques. Tools for addressing this problem in the literature have been based on either large sample results or prior knowledge of the parameter being estimated, with little guidance when these assumptions are not met...
August 9, 2017: Biometrical Journal. Biometrische Zeitschrift
Christina Habermehl, Axel Benner, Annette Kopp-Schneider
In recent years, numerous approaches for biomarker-based clinical trials have been developed. One of these developments are multiple-biomarker trials, which aim to investigate multiple biomarkers simultaneously in independent subtrials. For low-prevalence biomarkers, small sample sizes within the subtrials have to be expected, as well as many biomarker-negative patients at the screening stage. The small sample sizes may make it unfeasible to analyze the subtrials individually. This imposes the need to develop new approaches for the analysis of such trials...
August 1, 2017: Biometrical Journal. Biometrische Zeitschrift
Maral Saadati, Jan Beyersmann, Annette Kopp-Schneider, Axel Benner
We consider modeling competing risks data in high dimensions using a penalized cause-specific hazards (CSHs) approach. CSHs have conceptual advantages that are useful for analyzing molecular data. First, working on hazards level can further understanding of the underlying biological mechanisms that drive transition hazards. Second, CSH models can be used to extend the multistate framework for high-dimensional data. The CSH approach is implemented by fitting separate proportional hazards models for each event type (iCS)...
August 1, 2017: Biometrical Journal. Biometrische Zeitschrift
Siew Wan Hee, Nicholas Parsons, Nigel Stallard
The motivation for the work in this article is the setting in which a number of treatments are available for evaluation in phase II clinical trials and where it may be infeasible to try them concurrently because the intended population is small. This paper introduces an extension of previous work on decision-theoretic designs for a series of phase II trials. The program encompasses a series of sequential phase II trials with interim decision making and a single two-arm phase III trial. The design is based on a hybrid approach where the final analysis of the phase III data is based on a classical frequentist hypothesis test, whereas the trials are designed using a Bayesian decision-theoretic approach in which the unknown treatment effect is assumed to follow a known prior distribution...
July 26, 2017: Biometrical Journal. Biometrische Zeitschrift
Adél Lee, Aila Särkkä, Tara M Madhyastha, Thomas J Grabowski
We develop a two-stage spatial point process model that introduces new characterizations of activation patterns in multisubject functional Magnetic Resonance Imaging (fMRI) studies. Conventionally multisubject fMRI methods rely on combining information across subjects one voxel at a time in order to identify locations of peak activation in the brain. The two-stage model that we develop here addresses shortcomings of standard methods by explicitly modeling the spatial structure of functional signals and recognizing that corresponding cross-subject functional signals can be spatially misaligned...
July 12, 2017: Biometrical Journal. Biometrische Zeitschrift
Gabrielle Simoneau, Brooke Levis, Pim Cuijpers, John P A Ioannidis, Scott B Patten, Ian Shrier, Charles H Bombardier, Flavia de Lima Osório, Jesse R Fann, Dwenda Gjerdingen, Femke Lamers, Manote Lotrakul, Bernd Löwe, Juwita Shaaban, Lesley Stafford, Henk C P M van Weert, Mary A Whooley, Karin A Wittkampf, Albert S Yeung, Brett D Thombs, Andrea Benedetti
Individual patient data (IPD) meta-analyses are increasingly common in the literature. In the context of estimating the diagnostic accuracy of ordinal or semi-continuous scale tests, sensitivity and specificity are often reported for a given threshold or a small set of thresholds, and a meta-analysis is conducted via a bivariate approach to account for their correlation. When IPD are available, sensitivity and specificity can be pooled for every possible threshold. Our objective was to compare the bivariate approach, which can be applied separately at every threshold, to two multivariate methods: the ordinal multivariate random-effects model and the Poisson correlated gamma-frailty model...
July 10, 2017: Biometrical Journal. Biometrische Zeitschrift
Adrian Quintero, Emmanuel Lesaffre
Multivariate regression methods generally assume a constant covariance matrix for the observations. In case a heteroscedastic model is needed, the parametric and nonparametric covariance regression approaches can be restrictive in the literature. We propose a multilevel regression model for the mean and covariance structure, including random intercepts in both components and allowing for correlation between them. The implied conditional covariance function can be different across clusters as a result of the random effect in the variance structure...
July 10, 2017: Biometrical Journal. Biometrische Zeitschrift
Nicole H Augustin, Sung Won Kim, Annemarie Uhlig, Christina Hanser, Michael Henke, Martin Schumacher
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 that takes account of the longitudinal course of oral mucositis at different mouth sites and of the radiation dosage (in terms of cumulative dose)...
July 10, 2017: Biometrical Journal. Biometrische Zeitschrift
Saverio Ranciati, Cinzia Viroli, Ernst C Wit
Model-based clustering is a technique widely used to group a collection of units into mutually exclusive groups. There are, however, situations in which an observation could in principle belong to more than one cluster. In the context of next-generation sequencing (NGS) experiments, for example, the signal observed in the data might be produced by two (or more) different biological processes operating together and a gene could participate in both (or all) of them. We propose a novel approach to cluster NGS discrete data, coming from a ChIP-Seq experiment, with a mixture model, allowing each unit to belong potentially to more than one group: these multiple allocation clusters can be flexibly defined via a function combining the features of the original groups without introducing new parameters...
June 30, 2017: Biometrical Journal. Biometrische Zeitschrift
Elisa Duarte, Bruno de Sousa, Carmen Cadarso-Suárez, Nadja Klein, Thomas Kneib, Vítor Rodrigues
Studies addressing breast cancer risk factors have been looking at trends relative to age at menarche and menopause. These studies point to a downward trend of age at menarche and an upward trend for age at menopause, meaning an increase of a woman's reproductive lifespan cycle. In addition to studying the effect of the year of birth on the expectation of age at menarche and a woman's reproductive lifespan, it is important to understand how a woman's cohort affects the correlation between these two variables...
June 29, 2017: Biometrical Journal. Biometrische Zeitschrift
Stefan Wellek
No abstract text is available yet for this article.
June 29, 2017: Biometrical Journal. Biometrische Zeitschrift
Laura Schlieker, Anna Telaar, Angelika Lueking, Peter Schulz-Knappe, Carmen Theek, Katja Ickstadt
The classification of a population by a specific trait is a major task in medicine, for example when in a diagnostic setting groups of patients with specific diseases are identified, but also when in predictive medicine a group of patients is classified into specific disease severity classes that might profit from different treatments. When the sizes of those subgroups become small, for example in rare diseases, imbalances between the classes are more the rule than the exception and make statistical classification problematic when the error rate of the minority class is high...
June 19, 2017: Biometrical Journal. Biometrische Zeitschrift
Vahid Nassiri, Anna Ivanova, Geert Molenberghs, Geert Verbeke
A fast way is proposed based on the multiple outputation idea (Hoffman et al., ; Follmann et al., ) to calculate the precision of parameter estimates for high-dimensional multivariate joint models using a pairwise approach (Fieuws and Verbeke, ; Fieuws et al., ). Simulation results as well as data analysis shows possibly more than 2500 times faster computations using the proposed method. In our real data illustration, the time gain is more than 330 times.
June 16, 2017: Biometrical Journal. Biometrische Zeitschrift
Yasutaka Chiba
Fisher's exact test is commonly used to compare two groups when the outcome is binary in randomized trials. In the context of causal inference, this test explores the sharp causal null hypothesis (i.e. the causal effect of treatment is the same for all subjects), but not the weak causal null hypothesis (i.e. the causal risks are the same in the two groups). Therefore, in general, rejection of the null hypothesis by Fisher's exact test does not mean that the causal risk difference is not zero. Recently, Chiba (Journal of Biometrics and Biostatistics 2015; 6: 244) developed a new exact test for the weak causal null hypothesis when the outcome is binary in randomized trials; the new test is not based on any large sample theory and does not require any assumption...
June 12, 2017: Biometrical Journal. Biometrische Zeitschrift
Alessio Farcomeni
We introduce a penalized likelihood form for latent Markov models. We motivate its use for biomedical applications where the sample size is in the order of the tens, or at most hundreds, and there are only few repeated measures. The resulting estimates never break down, while spurious solutions are often obtained by maximizing the likelihood itself. We discuss model choice based on the Takeuchi Information Criterion. Simulations and a real-data application to monitoring serum Calcium levels in end-stage kidney disease are used for illustration...
June 8, 2017: Biometrical Journal. Biometrische Zeitschrift
Fulvio De Santis
No abstract text is available yet for this article.
May 26, 2017: Biometrical Journal. Biometrische Zeitschrift
Werner Brannath
No abstract text is available yet for this article.
May 26, 2017: Biometrical Journal. Biometrische Zeitschrift
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