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International Journal of Biostatistics

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https://read.qxmd.com/read/30811344/double-robust-efficient-estimators-of-longitudinal-treatment-effects-comparative-performance-in-simulations-and-a-case-study
#1
Linh Tran, Constantin Yiannoutsos, Kara Wools-Kaloustian, Abraham Siika, Mark van der Laan, Maya Petersen
A number of sophisticated estimators of longitudinal effects have been proposed for estimating the intervention-specific mean outcome. However, there is a relative paucity of research comparing these methods directly to one another. In this study, we compare various approaches to estimating a causal effect in a longitudinal treatment setting using both simulated data and data measured from a human immunodeficiency virus cohort. Six distinct estimators are considered: (i) an iterated conditional expectation representation, (ii) an inverse propensity weighted method, (iii) an augmented inverse propensity weighted method, (iv) a double robust iterated conditional expectation estimator, (v) a modified version of the double robust iterated conditional expectation estimator, and (vi) a targeted minimum loss-based estimator...
February 26, 2019: International Journal of Biostatistics
https://read.qxmd.com/read/30779702/variational-inference-for-coupled-hidden-markov-models-applied-to-the-joint-detection-of-copy-number-variations
#2
Xiaoqiang Wang, Emilie Lebarbier, Julie Aubert, Stéphane Robin
Hidden Markov models provide a natural statistical framework for the detection of the copy number variations (CNV) in genomics. In this context, we define a hidden Markov process that underlies all individuals jointly in order to detect and to classify genomics regions in different states (typically, deletion, normal or amplification). Structural variations from different individuals may be dependent. It is the case in agronomy where varietal selection program exists and species share a common phylogenetic past...
February 19, 2019: International Journal of Biostatistics
https://read.qxmd.com/read/30726189/the-performance-of-fixed-horizon-look-ahead-procedures-compared-to-backward-induction-in-bayesian-adaptive-randomization-decision-theoretic-clinical-trial-design
#3
Ari M Lipsky, Roger J Lewis
Designing optimal, Bayesian decision-theoretic trials has traditionally required the use of computationally-intensive backward induction. While methods for addressing this barrier have been put forward, few are both computationally tractable and non-myopic, with applications of the Gittins index being one notable example. Here we explore the look-ahead approach with adaptive-randomization, with designs ranging from the fully myopic to the fully informed. We compare the operating characteristics of the look-ahead designed trials, in which decision rules are based on a fixed number of future blocks, with those of trials designed using traditional backward induction...
February 6, 2019: International Journal of Biostatistics
https://read.qxmd.com/read/30648668/hazard-ratio-estimators-after-terminating-observation-within-matched-pairs-in-sibling-and-propensity-score-matched-designs
#4
Tomohiro Shinozaki, Mohammad Ali Mansournia
Similar to unmatched cohort studies, matched cohort studies may suffer from the censoring of events prior to the end of follow-up. Moreover, in some matched-pair cohort studies, observation time is prematurely terminated immediately after the follow-up of his/her matched member is completed by an event or censoring. Although the follow-up termination within matched pairs may or may not change the hazard ratio estimators, when and how the change occurs has not been clarified. We study the change in the estimates of the hazard ratio conditional on matched pairs and/or covariates by considering two types of matched-pair designs in cohort studies-sibling pair matching and propensity score matching-in which termination can be naturally considered...
January 15, 2019: International Journal of Biostatistics
https://read.qxmd.com/read/30864410/parametric-regression-analysis-with-covariate-misclassification-in-main-study-validation-study-designs
#5
Grace Y Yi, Ying Yan, Xiaomei Liao, Donna Spiegelman
Measurement error and misclassification have long been a concern in many fields, including medicine, administrative health care data, epidemiology, and survey sampling. It is known that measurement error and misclassification may seriously degrade the quality of estimation and inference, and should be avoided whenever possible. However, in practice, it is inevitable that measurements contain error for a variety of reasons. It is thus necessary to develop statistical strategies to cope with this issue. Although many inference methods have been proposed in the literature to address mis-measurement effects, some important issues remain unexplored...
December 15, 2018: International Journal of Biostatistics
https://read.qxmd.com/read/30471221/optimal-and-or-efficient-two-treatment-crossover-designs-for-five-carryover-models
#6
Jigneshkumar Gondaliya, Jyoti Divecha
Crossover designs robust to changes in carryover models are useful in clinical trials where the nature of carryover effects is not known in advance. The designs have been characterized for being optimal and efficient under no carryover-, traditional-, and, self and mixed carryover- models, however, ignoring the number of subjects, which has significant impact on both optimality and administrative convenience. In this article, adding two more practical models, the traditional, and, self and mixed carryover models having carryover effect only for the new or test treatment, a 5M algorithm is presented...
November 24, 2018: International Journal of Biostatistics
https://read.qxmd.com/read/30465718/a-serious-flaw-in-nutrition-epidemiology-a-meta-analysis-study
#7
Karl E Peace, JingJing Yin, Haresh Rochani, Sarbesh Pandeya, Stanley Young
Background Many researchers have studied the relationship between diet and health. Specifically, there are papers showing an association between the consumption of sugar sweetened beverages and Type 2 diabetes. Many meta-analyses use individual studies that do not attempt to adjust for multiple testing or multiple modeling. Hence the claims reported in a meta-analysis paper may be unreliable as the base papers do not ensure unbiased statistics. Objective Determine (i) the statistical reliability of 10 papers and (ii) indirectly the reliability of the meta-analysis study...
November 22, 2018: International Journal of Biostatistics
https://read.qxmd.com/read/30379638/maximum-likelihood-estimation-in-a-semicontinuous-survival-model-with-covariates-subject-to-detection-limits
#8
Paul W Bernhardt
Semicontinuous data are common in biological studies, occurring when a variable is continuous over a region but has a point mass at one or more points. In the motivating Genetic and Inflammatory Markers of Sepsis (GenIMS) study, it was of interest to determine how several biomarkers subject to detection limits were related to survival for patients entering the hospital with community acquired pneumonia. While survival times were recorded for all individuals in the study, the primary endpoint of interest was the binary event of 90-day survival, and no patients were lost to follow-up prior to 90 days...
October 31, 2018: International Journal of Biostatistics
https://read.qxmd.com/read/30173203/estimating-causal-effects-from-nonparanormal-observational-data
#9
Seyed Mahdi Mahmoudi, Ernst C Wit
One of the basic aims of science is to unravel the chain of cause and effect of particular systems. Especially for large systems, this can be a daunting task. Detailed interventional and randomized data sampling approaches can be used to resolve the causality question, but for many systems, such interventions are impossible or too costly to obtain. Recently, Maathuis et al. (2010), following ideas from Spirtes et al. (2000), introduced a framework to estimate causal effects in large scale Gaussian systems...
September 1, 2018: International Journal of Biostatistics
https://read.qxmd.com/read/30048236/a-truncation-model-for-estimating-species-richness
#10
Babagnidé François Koladjo, Mesrob I Ohannessian, Elisabeth Gassiat
We propose a truncation model for the abundance distribution in species richness estimation. This model is inherently semiparametric and incorporates an unknown truncation threshold between rare and abundant observations. Using the conditional likelihood, we derive a class of estimators for the parameters in this model by stepwise maximization. The species richness estimator is given by the integer maximizing the binomial likelihood, given all other parameters in the model. Under regularity conditions, we show that our estimators of the model parameters are asymptotically efficient...
July 26, 2018: International Journal of Biostatistics
https://read.qxmd.com/read/30024852/a-new-class-of-robust-two-sample-wald-type-tests
#11
Abhik Ghosh, Nirian Martin, Ayanendranath Basu, Leandro Pardo
Parametric hypothesis testing associated with two independent samples arises frequently in several applications in biology, medical sciences, epidemiology, reliability and many more. In this paper, we propose robust Wald-type tests for testing such two sample problems using the minimum density power divergence estimators of the underlying parameters. In particular, we consider the simple two-sample hypothesis concerning the full parametric homogeneity as well as the general two-sample (composite) hypotheses involving some nuisance parameters...
July 19, 2018: International Journal of Biostatistics
https://read.qxmd.com/read/29981281/a-spatio-temporal-model-and-inference-tools-for-longitudinal-count-data-on-multicolor-cell-growth
#12
PuXue Qiao, Christina Mølck, Davide Ferrari, Frédéric Hollande
Multicolor cell spatio-temporal image data have become important to investigate organ development and regeneration, malignant growth or immune responses by tracking different cell types both in vivo and in vitro. Statistical modeling of image data from common longitudinal cell experiments poses significant challenges due to the presence of complex spatio-temporal interactions between different cell types and difficulties related to measurement of single cell trajectories. Current analysis methods focus mainly on univariate cases, often not considering the spatio-temporal effects affecting cell growth between different cell populations...
July 7, 2018: International Journal of Biostatistics
https://read.qxmd.com/read/29906269/a-fast-and-robust-way-to-estimate-overlap-of-niches-and-draw-inference
#13
Judith H Parkinson, Raoul Kutil, Jonas Kuppler, Robert R Junker, Wolfgang Trutschnig, Arne C Bathke
The problem of quantifying the overlap of Hutchinsonian niches has received much attention lately, in particular in quantitative ecology, from where it also originates. However, the niche concept has the potential to also be useful in many other application areas, as for example in economics. We are presenting a fully nonparametric, robust solution to this problem, along with exact shortcut formulas based on rank-statistics, and with a rather intuitive probabilistic interpretation. Furthermore, by deriving the asymptotic sampling distribution of the estimators, we are proposing the first asymptotically valid inference method, providing confidence intervals for the niche overlap...
June 15, 2018: International Journal of Biostatistics
https://read.qxmd.com/read/29883322/marginal-structural-models-with-counterfactual-effect-modifiers
#14
Wenjing Zheng, Zhehui Luo, Mark J van der Laan
In health and social sciences, research questions often involve systematic assessment of the modification of treatment causal effect by patient characteristics. In longitudinal settings, time-varying or post-intervention effect modifiers are also of interest. In this work, we investigate the robust and efficient estimation of the Counterfactual-History-Adjusted Marginal Structural Model (van der Laan MJ, Petersen M. Statistical learning of origin-specific statically optimal individualized treatment rules. Int J Biostat...
June 8, 2018: International Journal of Biostatistics
https://read.qxmd.com/read/29878883/unfolding-the-genome-the-case-study-of-p-falciparum
#15
Nelle Varoquaux
The development of new ways to probe samples for the three-dimensional (3D) structure of DNA paves the way for in depth and systematic analyses of the genome architecture. 3C-like methods coupled with high-throughput sequencing can now assess physical interactions between pairs of loci in a genome-wide fashion, thus enabling the creation of genome-by-genome contact maps. The spreading of such protocols creates many new opportunities for methodological development: how can we infer 3D models from these contact maps? Can such models help us gain insights into biological processes? Several recent studies applied such protocols to P...
June 7, 2018: International Journal of Biostatistics
https://read.qxmd.com/read/29676993/nonparametric-interval-estimators-for-the-coefficient-of-variation
#16
Dongliang Wang, Margaret K Formica, Song Liu
The coefficient of variation (CV) is a widely used scaleless measure of variability in many disciplines. However the inference for the CV is limited to parametric methods or standard bootstrap. In this paper we propose two nonparametric methods aiming to construct confidence intervals for the coefficient of variation. The first one is to apply the empirical likelihood after transforming the original data. The second one is a modified jackknife empirical likelihood method. We also propose bootstrap procedures for calibrating the test statistics...
April 19, 2018: International Journal of Biostatistics
https://read.qxmd.com/read/29621006/a-bayesian-framework-for-estimating-the-concordance-correlation-coefficient-using-skew-elliptical-distributions
#17
Dai Feng, Richard Baumgartner, Vladimir Svetnik
The concordance correlation coefficient (CCC) is a widely used scaled index in the study of agreement. In this article, we propose estimating the CCC by a unified Bayesian framework that can (1) accommodate symmetric or asymmetric and light- or heavy-tailed data; (2) select model from several candidates; and (3) address other issues frequently encountered in practice such as confounding covariates and missing data. The performance of the proposal was studied and demonstrated using simulated as well as real-life biomarker data from a clinical study of an insomnia drug...
April 5, 2018: International Journal of Biostatistics
https://read.qxmd.com/read/29517976/notes-on-test-and-estimation-in-comparison-of-three-treatments-under-a-simple-carry-over-three-period-model
#18
Kung-Jong Lui
Under the three-treatment three-period crossover design with simple carry-over effects, we derive the least-squares estimators for period effects, treatment effects and carry-over effects, as well as their covariance matrix in closed and explicit expressions. Using Monte Carlo simulation, we compare the test procedure adjusting carry-over with that ignoring carry-over with respect to Type I error and power. We further compare interval estimators adjusting carry-over with those ignoring carry-over with respect to the coverage probability and the average length...
March 7, 2018: International Journal of Biostatistics
https://read.qxmd.com/read/29389664/joint-models-of-longitudinal-and-time-to-event-data-with-more-than-one-event-time-outcome-a-review
#19
Graeme L Hickey, Pete Philipson, Andrea Jorgensen, Ruwanthi Kolamunnage-Dona
Methodological development and clinical application of joint models of longitudinal and time-to-event outcomes have grown substantially over the past two decades. However, much of this research has concentrated on a single longitudinal outcome and a single event time outcome. In clinical and public health research, patients who are followed up over time may often experience multiple, recurrent, or a succession of clinical events. Models that utilise such multivariate event time outcomes are quite valuable in clinical decision-making...
January 31, 2018: International Journal of Biostatistics
https://read.qxmd.com/read/29306919/zero-inflated-conway-maxwell-poisson-distribution-to-analyze-discrete-data
#20
Shin Zhu Sim, Ramesh C Gupta, Seng Huat Ong
In this paper, we study the zero-inflated Conway-Maxwell Poisson (ZICMP) distribution and develop a regression model. Score and likelihood ratio tests are also implemented for testing the inflation/deflation parameter. Simulation studies are carried out to examine the performance of these tests. A data example is presented to illustrate the concepts. In this example, the proposed model is compared to the well-known zero-inflated Poisson (ZIP) and the zero- inflated generalized Poisson (ZIGP) regression models...
January 9, 2018: International Journal of Biostatistics
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