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Statistical Methods in Medical Research

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https://www.readbyqxmd.com/read/27899706/mixed-hidden-markov-quantile-regression-models-for-longitudinal-data-with-possibly-incomplete-sequences
#1
Maria Francesca Marino, Nikos Tzavidis, Marco Alfò
Quantile regression provides a detailed and robust picture of the distribution of a response variable, conditional on a set of observed covariates. Recently, it has be been extended to the analysis of longitudinal continuous outcomes using either time-constant or time-varying random parameters. However, in real-life data, we frequently observe both temporal shocks in the overall trend and individual-specific heterogeneity in model parameters. A benchmark dataset on HIV progression gives a clear example. Here, the evolution of the CD4 log counts exhibits both sudden temporal changes in the overall trend and heterogeneity in the effect of the time since seroconversion on the response dynamics...
November 28, 2016: Statistical Methods in Medical Research
https://www.readbyqxmd.com/read/27895266/a-simple-method-to-estimate-the-time-dependent-receiver-operating-characteristic-curve-and-the-area-under-the-curve-with-right-censored-data
#2
Liang Li, Tom Greene, Bo Hu
The time-dependent receiver operating characteristic curve is often used to study the diagnostic accuracy of a single continuous biomarker, measured at baseline, on the onset of a disease condition when the disease onset may occur at different times during the follow-up and hence may be right censored. Due to right censoring, the true disease onset status prior to the pre-specified time horizon may be unknown for some patients, which causes difficulty in calculating the time-dependent sensitivity and specificity...
November 27, 2016: Statistical Methods in Medical Research
https://www.readbyqxmd.com/read/27885051/linear-rank-testing-of-a-non-binary-responder-analysis-efficacy-score-to-evaluate-pharmacotherapies-for-substance-use-disorders
#3
Tyson H Holmes, Shou-Hua Li, David J McCann
The design of pharmacological trials for management of substance use disorders is shifting toward outcomes of successful individual-level behavior (abstinence or no heavy use). While binary success/failure analyses are common, McCann and Li (CNS Neurosci Ther 2012; 18: 414-418) introduced "number of beyond-threshold weeks of success" (NOBWOS) scores to avoid dichotomized outcomes. NOBWOS scoring employs an efficacy "hurdle" with values reflecting duration of success. Here, we evaluate NOBWOS scores rigorously...
November 23, 2016: Statistical Methods in Medical Research
https://www.readbyqxmd.com/read/27872194/sample-size-and-power-for-a-stratified-doubly-randomized-preference-design
#4
Briana Cameron, Denise A Esserman
The two-stage (or doubly) randomized preference trial design is an important tool for researchers seeking to disentangle the role of patient treatment preference on treatment response through estimation of selection and preference effects. Up until now, these designs have been limited by their assumption of equal preference rates and effect sizes across the entire study population. We propose a stratified two-stage randomized trial design that addresses this limitation. We begin by deriving stratified test statistics for the treatment, preference, and selection effects...
November 21, 2016: Statistical Methods in Medical Research
https://www.readbyqxmd.com/read/27856963/variable-selection-for-mixture-and-promotion-time-cure-rate-models
#5
Abdullah Masud, Wanzhu Tu, Zhangsheng Yu
Failure-time data with cured patients are common in clinical studies. Data from these studies are typically analyzed with cure rate models. Variable selection methods have not been well developed for cure rate models. In this research, we propose two least absolute shrinkage and selection operators based methods, for variable selection in mixture and promotion time cure models with parametric or nonparametric baseline hazards. We conduct an extensive simulation study to assess the operating characteristics of the proposed methods...
November 16, 2016: Statistical Methods in Medical Research
https://www.readbyqxmd.com/read/27856962/analysis-of-an-incomplete-longitudinal-composite-variable-using-a-marginalized-random-effects-model-and-multiple-imputation
#6
Masahiko Gosho, Kazushi Maruo, Ryota Ishii, Akihiro Hirakawa
The total score, which is calculated as the sum of scores in multiple items or questions, is repeatedly measured in longitudinal clinical studies. A mixed effects model for repeated measures method is often used to analyze these data; however, if one or more individual items are not measured, the method cannot be directly applied to the total score. We develop two simple and interpretable procedures that infer fixed effects for a longitudinal continuous composite variable. These procedures consider that the items that compose the total score are multivariate longitudinal continuous data and, simultaneously, handle subject-level and item-level missing data...
November 16, 2016: Statistical Methods in Medical Research
https://www.readbyqxmd.com/read/27856961/a-novel-nonparametric-confidence-interval-for-differences-of-proportions-for-correlated-binary-data
#7
Chongyang Duan, Yingshu Cao, Lizhi Zhou, Ming T Tan, Pingyan Chen
Various confidence interval estimators have been developed for differences in proportions resulted from correlated binary data. However, the width of the mostly recommended Tango's score confidence interval tends to be wide, and the computing burden of exact methods recommended for small-sample data is intensive. The recently proposed rank-based nonparametric method by treating proportion as special areas under receiver operating characteristic provided a new way to construct the confidence interval for proportion difference on paired data, while the complex computation limits its application in practice...
November 16, 2016: Statistical Methods in Medical Research
https://www.readbyqxmd.com/read/27856960/the-asymptotic-maximal-procedure-for-subject-randomization-in-clinical-trials
#8
Wenle Zhao, Vance W Berger, Zhenning Yu
The maximal procedure is a restricted randomization method that maximizes the number of feasible allocation sequences under the constraints of the maximum tolerated imbalance and the allocation sequence length. It assigns an equal probability to all feasible sequences. However, its implementation is not easy due to the lack of the Markovian property of the conditional allocation probabilities. In this paper, we propose the asymptotic maximal procedure, which replaces the sequence-length-dependent conditional allocation probabilities with their asymptotic values...
November 16, 2016: Statistical Methods in Medical Research
https://www.readbyqxmd.com/read/27856959/evolution-of-association-between-renal-and-liver-functions-while-awaiting-heart-transplant-an-application-using-a-bivariate-multiphase-nonlinear-mixed-effects-model
#9
Jeevanantham Rajeswaran, Eugene H Blackstone, John Barnard
In many longitudinal follow-up studies, we observe more than one longitudinal outcome. Impaired renal and liver functions are indicators of poor clinical outcomes for patients who are on mechanical circulatory support and awaiting heart transplant. Hence, monitoring organ functions while waiting for heart transplant is an integral part of patient management. Longitudinal measurements of bilirubin can be used as a marker for liver function and glomerular filtration rate for renal function. We derive an approximation to evolution of association between these two organ functions using a bivariate nonlinear mixed effects model for continuous longitudinal measurements, where the two submodels are linked by a common distribution of time-dependent latent variables and a common distribution of measurement errors...
November 16, 2016: Statistical Methods in Medical Research
https://www.readbyqxmd.com/read/27856958/sample-size-calculation-for-agreement-between-two-raters-with-binary-endpoints-using-exact-tests
#10
Guogen Shan
In an agreement test between two raters with binary endpoints, existing methods for sample size calculation are always based on asymptotic approaches that use limiting distributions of a test statistic under null and alternative hypotheses. These calculated sample sizes may be not reliable due to the unsatisfactory type I error control of asymptotic approaches. We propose a new sample size calculation based on exact approaches which control for the type I error rate. The two exact approaches are considered: one approach based on maximization and the other based on estimation and maximization...
November 16, 2016: Statistical Methods in Medical Research
https://www.readbyqxmd.com/read/27815495/diagnostic-checks-in-mixture-cure-models-with-interval-censoring
#11
Sylvie Scolas, Catherine Legrand, Abderrahim Oulhaj, Anouar El Ghouch
Models for interval-censored survival data presenting a fraction of "cure" or "immune" patients have recently been proposed in the literature, particularly extending the mixture cure model to interval-censored data. However, little is known about the goodness-of-fit of such models. In a mixture cure model, the survival distribution of the entire population is improper and expressed in terms of the survival distribution of uncured individuals, i.e. the latency part of the model, and the probability to experience the event of interest, i...
November 4, 2016: Statistical Methods in Medical Research
https://www.readbyqxmd.com/read/27807177/integrating-genomic-signatures-for-treatment-selection-with-bayesian-predictive-failure-time-models
#12
Junsheng Ma, Brian P Hobbs, Francesco C Stingo
Over the past decade, a tremendous amount of resources have been dedicated to the pursuit of developing genomic signatures that effectively match patients with targeted therapies. Although dozens of therapies that target DNA mutations have been developed, the practice of studying single candidate genes has limited our understanding of cancer. Moreover, many studies of multiple-gene signatures have been conducted for the purpose of identifying prognostic risk cohorts, and thus are limited for selecting personalized treatments...
November 1, 2016: Statistical Methods in Medical Research
https://www.readbyqxmd.com/read/27789653/dynamic-longitudinal-discriminant-analysis-using-multiple-longitudinal-markers-of-different-types
#13
David M Hughes, Arnošt Komárek, Gabriela Czanner, Marta Garcia-Fiñana
There is an emerging need in clinical research to accurately predict patients' disease status and disease progression by optimally integrating multivariate clinical information. Clinical data are often collected over time for multiple biomarkers of different types (e.g. continuous, binary and counts). In this paper, we present a flexible and dynamic (time-dependent) discriminant analysis approach in which multiple biomarkers of various types are jointly modelled for classification purposes by the multivariate generalized linear mixed model...
October 26, 2016: Statistical Methods in Medical Research
https://www.readbyqxmd.com/read/27705884/unified-approach-for-extrapolation-and-bridging-of-adult-information-in-early-phase-dose-finding-paediatric-studies
#14
Caroline Petit, Adeline Samson, Satoshi Morita, Moreno Ursino, Jérémie Guedj, Vincent Jullien, Emmanuelle Comets, Sarah Zohar
The number of trials conducted and the number of patients per trial are typically small in paediatric clinical studies. This is due to ethical constraints and the complexity of the medical process for treating children. While incorporating prior knowledge from adults may be extremely valuable, this must be done carefully. In this paper, we propose a unified method for designing and analysing dose-finding trials in paediatrics, while bridging information from adults. The dose-range is calculated under three extrapolation options, linear, allometry and maturation adjustment, using adult pharmacokinetic data...
October 4, 2016: Statistical Methods in Medical Research
https://www.readbyqxmd.com/read/27705883/effective-plots-to-assess-bias-and-precision-in-method-comparison-studies
#15
Patrick Taffé
Bland and Altman's limits of agreement have traditionally been used in clinical research to assess the agreement between different methods of measurement for quantitative variables. However, when the variances of the measurement errors of the two methods are different, Bland and Altman's plot may be misleading; there are settings where the regression line shows an upward or a downward trend but there is no bias or a zero slope and there is a bias. Therefore, the goal of this paper is to clearly illustrate why and when does a bias arise, particularly when heteroscedastic measurement errors are expected, and propose two new plots, the "bias plot" and the "precision plot," to help the investigator visually and clinically appraise the performance of the new method...
October 4, 2016: Statistical Methods in Medical Research
https://www.readbyqxmd.com/read/27697838/estimation-after-blinded-sample-size-reassessment
#16
Martin Posch, Florian Klinglmueller, Franz König, Frank Miller
Blinded sample size reassessment is a popular means to control the power in clinical trials if no reliable information on nuisance parameters is available in the planning phase. We investigate how sample size reassessment based on blinded interim data affects the properties of point estimates and confidence intervals for parallel group superiority trials comparing the means of a normal endpoint. We evaluate the properties of two standard reassessment rules that are based on the sample size formula of the z-test, derive the worst case reassessment rule that maximizes the absolute mean bias and obtain an upper bound for the mean bias of the treatment effect estimate...
October 2, 2016: Statistical Methods in Medical Research
https://www.readbyqxmd.com/read/27683581/optimally-estimating-the-sample-mean-from-the-sample-size-median-mid-range-and-or-mid-quartile-range
#17
Dehui Luo, Xiang Wan, Jiming Liu, Tiejun Tong
The era of big data is coming, and evidence-based medicine is attracting increasing attention to improve decision making in medical practice via integrating evidence from well designed and conducted clinical research. Meta-analysis is a statistical technique widely used in evidence-based medicine for analytically combining the findings from independent clinical trials to provide an overall estimation of a treatment effectiveness. The sample mean and standard deviation are two commonly used statistics in meta-analysis but some trials use the median, the minimum and maximum values, or sometimes the first and third quartiles to report the results...
September 27, 2016: Statistical Methods in Medical Research
https://www.readbyqxmd.com/read/27659169/feasibility-of-reusing-time-matched-controls-in-an-overlapping-cohort
#18
Bénédicte Delcoigne, Niels Hagenbuch, Maria Ec Schelin, Agus Salim, Linda S Lindström, Jonas Bergh, Kamila Czene, Marie Reilly
The methods developed for secondary analysis of nested case-control data have been illustrated only in simplified settings in a common cohort and have not found their way into biostatistical practice. This paper demonstrates the feasibility of reusing prior nested case-control data in a realistic setting where a new outcome is available in an overlapping cohort where no new controls were gathered and where all data have been anonymised. Using basic information about the background cohort and sampling criteria, the new cases and prior data are "aligned" to identify the common underlying study base...
September 21, 2016: Statistical Methods in Medical Research
https://www.readbyqxmd.com/read/27659168/comparison-of-statistical-approaches-dealing-with-time-dependent-confounding-in-drug-effectiveness-studies
#19
Mohammad Ehsanul Karim, John Petkau, Paul Gustafson, Robert W Platt, Helen Tremlett
In longitudinal studies, if the time-dependent covariates are affected by the past treatment, time-dependent confounding may be present. For a time-to-event response, marginal structural Cox models are frequently used to deal with such confounding. To avoid some of the problems of fitting marginal structural Cox model, the sequential Cox approach has been suggested as an alternative. Although the estimation mechanisms are different, both approaches claim to estimate the causal effect of treatment by appropriately adjusting for time-dependent confounding...
September 21, 2016: Statistical Methods in Medical Research
https://www.readbyqxmd.com/read/27655806/inferring-marginal-association-with-paired-and-unpaired-clustered-data
#20
Douglas J Lorenz, Steven Levy, Somnath Datta
In the marginal analysis of clustered data, where the marginal distribution of interest is that of a typical observation within a typical cluster, analysis by reweighting has been introduced as a useful tool for estimating parameters of these marginal distributions. Such reweighting methods have foundation in within-cluster resampling schemes that marginalize potential informativeness due to cluster size or within-cluster covariate distribution, to which reweighting methods are asymptotically equivalent. In this paper, we introduce a reweighting scheme for the marginal analysis of clustered data that generalizes prior reweighting methods, with a particular application to measuring bivariate correlation in unpaired clustered data, in which observations of two random variables are not naturally paired at the within-cluster level...
September 20, 2016: Statistical Methods in Medical Research
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