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Biometrical Journal. Biometrische Zeitschrift

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https://www.readbyqxmd.com/read/30221408/observations-below-multiple-lower-limits-of-quantification-how-to-estimate-the-mean-and-variance
#1
Tanja Berger, Ralf-Dieter Hilgers, Nicole Heussen
Multiple lower limits of quantification (MLOQs) result if various laboratories are involved in the analysis of concentration data and some observations are too low to be quantified. For normally distributed data under MLOQs there exists only the multiple regression method of Helsel to estimate the mean and variance. We propose a simple imputation method and two new maximum likelihood estimation methods: the multiple truncated sample method and the multiple censored sample method. A simulation study is conducted to compare the performances of the newly introduced methods to Helsel's via the criteria root mean squared error (RMSE) and bias of the parameter estimates...
September 16, 2018: Biometrical Journal. Biometrische Zeitschrift
https://www.readbyqxmd.com/read/30221403/dynamic-clinical-prediction-models-for-discrete-time-to-event-data-with-competing-risks-a-case-study-on-the-outcomerea-database
#2
Rachel Heyard, Jean-François Timsit, Wafa Ibn Essaied, Leonhard Held
The development of clinical prediction models requires the selection of suitable predictor variables. Techniques to perform objective Bayesian variable selection in the linear model are well developed and have been extended to the generalized linear model setting as well as to the Cox proportional hazards model. Here, we consider discrete time-to-event data with competing risks and propose methodology to develop a clinical prediction model for the daily risk of acquiring a ventilator-associated pneumonia (VAP) attributed to P...
September 16, 2018: Biometrical Journal. Biometrische Zeitschrift
https://www.readbyqxmd.com/read/30209817/computing-individual-and-collective-ethical-utility-for-optimally-planning-phase-iii-trials
#3
Lucio De Capitani, Daniele De Martini
A quantitative evaluation of individual and collective ethics is proposed here, with the aim of providing a tool for sample size determination/estimation that goes further than the standard power setting of 80-90%. Individual ethics deal with issues that concern the patients enrolled in the trial, where collective ones concern the patients not enrolled in the trial, and who might benefit from a positive result. The global ethical utility (GEU) of a phase III trial is introduced here, being the summation of individual and collective ethical utilities, and can be viewed as a function of the sample size...
September 12, 2018: Biometrical Journal. Biometrische Zeitschrift
https://www.readbyqxmd.com/read/30209813/author-s-response-when-should-meta-analysis-avoid-making-hidden-normality-assumptions
#4
Dan Jackson, Ian R White
No abstract text is available yet for this article.
September 12, 2018: Biometrical Journal. Biometrische Zeitschrift
https://www.readbyqxmd.com/read/30203492/comparison-of-different-approaches-for-dose-response-analysis
#5
REVIEW
Saswati Saha, Werner Brannath
Characterizing an appropriate dose-response relationship and identifying the right dose in a clinical trial are two main goals of early drug-development. MCP-Mod is one of the pioneer approaches developed within the last 10 years that combines the modeling techniques with multiple comparison procedures to address the above goals in clinical drug development. The MCP-Mod approach begins with a set of potential dose-response models, tests for a significant dose-response effect (proof of concept, PoC) using multiple linear contrasts tests and selects the "best" model among those with a significant contrast test...
September 10, 2018: Biometrical Journal. Biometrische Zeitschrift
https://www.readbyqxmd.com/read/30198195/estimation-of-adjusted-expected-excess-length-of-stay-associated-with-ventilation-acquired-pneumonia-in-intensive-care-a-multistate-approach-accounting-for-time-dependent-mechanical-ventilation
#6
Tobias Bluhmki, Arthur Allignol, Stephane Ruckly, Jean-Francois Timsit, Martin Wolkewitz, Jan Beyersmann
The expected excess length-of-stay is an established concept to assess the health and economic impact of nosocomial, that is, hospital-acquired infections such as ventilation-acquired pneumonia in intensive care. Estimation must account for the timing of infection as in a multistate perspective, because common retrospective comparisons yield inflated estimates due to time-dependent bias. Since occurrence of ventilation-acquired pneumonia is closely linked to ventilation status, we suggest a multistate model incorporating time-dependent mechanical ventilation as additional states...
September 9, 2018: Biometrical Journal. Biometrische Zeitschrift
https://www.readbyqxmd.com/read/30187522/hommel-s-procedure-in-linear-time
#7
Rosa J Meijer, Thijmen J P Krebs, Jelle J Goeman
Hommel's and Hochberg's procedures for familywise error control are both derived as shortcuts in a closed testing procedure with the Simes local test. Hommel's shortcut is exact but takes quadratic time in the number of hypotheses. Hochberg's shortcut takes only linear time after the P-values are sorted, but is conservative. In this paper, we present an exact shortcut in linear time on sorted P-values, combining the strengths of both procedures. The novel shortcut also applies to a robust variant of Hommel's procedure that does not require the assumption of the Simes inequality...
September 5, 2018: Biometrical Journal. Biometrische Zeitschrift
https://www.readbyqxmd.com/read/30182372/optimal-sample-size-allocation-and-go-no-go-decision-rules-for-phase-ii-iii-programs-where-several-phase-iii-trials-are-performed
#8
Stella Preussler, Meinhard Kieser, Marietta Kirchner
The conduct of phase II and III programs is costly, time-consuming and, due to high failure rates in late development stages, risky. There is a strong connection between phase II and III trials as the go/no-go decision and the sample size chosen for phase III are based on the results observed in phase II. An integrated planning of phase II and III is therefore reasonable. The success of phase II/III programs crucially depends on the allocation of the resources to phase II and III in terms of sample size and the rule applied to decide whether to stop or to proceed with phase III...
September 5, 2018: Biometrical Journal. Biometrische Zeitschrift
https://www.readbyqxmd.com/read/30178528/a-combined-proof-of-concept-and-dose-finding-study-with-multiple-endpoints-a-bayesian-adaptive-design-in-chronic-prostatitis-chronic-pelvic-pain-syndrome
#9
Reynaldo Martina, Jos Houbiers, Joost Melis, Olivier van Till
There is a need for identifying effective drugs or terminating ineffective drugs as early as possible to optimize efficient and cost effective drug development. The aim of the proposed trial was to simultaneously establish Proof of Concept (PoC) and dose finding (DF) for a new drug with a novel mode of action in a new indication. We simulated and executed an adaptive allocation design to investigate the effects of a drug on male patients suffering from chronic prostatitis/chronic pelvic pain syndrome (CP/CPPS)...
September 3, 2018: Biometrical Journal. Biometrische Zeitschrift
https://www.readbyqxmd.com/read/30175406/biases-incurred-from-nonrandom-repeat-testing-of-haemoglobin-levels-in-blood-donors-selective-testing-and-its-implications
#10
Ryan K Chung, Angela M Wood, Michael J Sweeting
To help prevent anaemia, it is a requisite for blood donors to undergo a haemoglobin test to ensure levels are not too low before donation. It is therefore important to have an accurate testing device and strategy to ensure donors are not being inappropriately bled. A recent study in blood donors used a selective testing strategy where if a donor's haemoglobin level is below the level required for donation, then another reading is taken and if this occurs again, a third and final reading is used. This strategy can reduce the average number of readings required per donor compared to taking three measurements for all donors...
September 2, 2018: Biometrical Journal. Biometrische Zeitschrift
https://www.readbyqxmd.com/read/30175405/monitoring-futility-and-efficacy-in-phase-ii-trials-with-bayesian-posterior-distributions-a-calibration-approach
#11
Annette Kopp-Schneider, Manuel Wiesenfarth, Ruth Witt, Dominic Edelmann, Olaf Witt, Ulrich Abel
A multistage single arm phase II trial with binary endpoint is considered. Bayesian posterior probabilities are used to monitor futility in interim analyses and efficacy in the final analysis. For a beta-binomial model, decision rules based on Bayesian posterior probabilities are converted to "traditional" decision rules in terms of number of responders among patients observed so far. Analytical derivations are given for the probability of stopping for futility and for the probability to declare efficacy...
September 2, 2018: Biometrical Journal. Biometrische Zeitschrift
https://www.readbyqxmd.com/read/30151835/equivalence-analyses-of-dissolution-profiles-with-the-mahalanobis-distance
#12
Thomas Hoffelder
For some postapproval changes, the manufacturer has to demonstrate that the dissolution profile of the drug product before the change is statistically equivalent to the dissolution profile after the change. Guidelines suggest the so-called similarity factor f2 as standard approach for the equivalence analysis. f2 is a statistically questionable transformation of the Euclidean distance between both profile means and does not allow a control of the type I error rate. An alternative multivariate distance measure for quantifying the dissimilarity between both profile groups is the Mahalanobis distance...
August 27, 2018: Biometrical Journal. Biometrische Zeitschrift
https://www.readbyqxmd.com/read/30136415/ridge-estimation-of-network-models-from-time-course-omics-data
#13
Viktorian Miok, Saskia M Wilting, Wessel N van Wieringen
Time-course omics experiments enable the reconstruction of the dynamics of the cellular regulatory network. Here, we describe the means for this reconstruction and the downstream exploitation of the inferred network. It is assumed that one of the various vector-autoregressive models (VAR) models presented here serves as a reasonably accurate description of the time-course omics data. The models are estimated through ridge penalized likelihood maximization, accompanied by functionality for the determination of optimal penalty paramaters...
August 22, 2018: Biometrical Journal. Biometrische Zeitschrift
https://www.readbyqxmd.com/read/30117183/a-note-on-pseudo-observations-and-left-truncation
#14
Mia K Grand, Hein Putter, Arthur Allignol, Per K Andersen
Pseudo-observations have been introduced as a way to perform regression analysis of a mean value parameter related to a right-censored time-to-event outcome, such as the survival probability or the restricted mean survival time. Since the introduction of the approach there have been several extensions from the original setting. However, the proper definition and performance of pseudo-observations under left-truncation has not yet been addressed. Here, we look at two types of pseudo-observations under right-censoring and left-truncation...
August 16, 2018: Biometrical Journal. Biometrische Zeitschrift
https://www.readbyqxmd.com/read/30101466/contribution-to-the-discussion-of-when-should-meta-analysis-avoid-making-hidden-normality-assumptions
#15
Christopher H Schmid
No abstract text is available yet for this article.
August 12, 2018: Biometrical Journal. Biometrische Zeitschrift
https://www.readbyqxmd.com/read/30101441/contribution-to-the-discussion-of-when-should-meta-analysis-avoid-making-hidden-normality-assumptions
#16
Heinz Holling
No abstract text is available yet for this article.
August 12, 2018: Biometrical Journal. Biometrische Zeitschrift
https://www.readbyqxmd.com/read/30101421/an-approximate-bayesian-significance-test-for-genomic-evaluations
#17
Dörte Wittenburg, Volkmar Liebscher
Genomic information can be used to study the genetic architecture of some trait. Not only the size of the genetic effect captured by molecular markers and their position on the genome but also the mode of inheritance, which might be additive or dominant, and the presence of interactions are interesting parameters. When searching for interacting loci, estimating the effect size and determining the significant marker pairs increases the computational burden in terms of speed and memory allocation dramatically...
August 12, 2018: Biometrical Journal. Biometrische Zeitschrift
https://www.readbyqxmd.com/read/30091155/contribution-to-the-discussion-of-when-should-meta-analysis-avoid-making-hidden-normality-assumptions
#18
Federico Ambrogi, Matteo Rota
No abstract text is available yet for this article.
August 8, 2018: Biometrical Journal. Biometrische Zeitschrift
https://www.readbyqxmd.com/read/30088289/contribution-to-the-discussion-of-when-should-meta-analysis-avoid-making-hidden-normality-assumptions
#19
Peter Schlattmann
No abstract text is available yet for this article.
August 7, 2018: Biometrical Journal. Biometrische Zeitschrift
https://www.readbyqxmd.com/read/30088287/contribution-to-the-discussion-of-when-should-meta-analysis-avoid-making-hidden-normality-assumptions
#20
Ralf Bender, Lars Beckmann
No abstract text is available yet for this article.
August 7, 2018: Biometrical Journal. Biometrische Zeitschrift
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