Abstract:
:We provide a Bayesian analysis of data categorized into two levels of age (younger than 50 years, at least 50 years) and three levels of bone mineral density (normal, osteopenia, osteoporosis) for white females at least 20 years old in the third National Health and Nutrition Examination Survey. For the sample, the age of each individual is known, but some individuals did not have their BMD measured. We use two types of models: In the ignorable non-response models the propensity to respond does not depend on BMD and age of an individual, while in the non-ignorable non-response models it does. These are the baseline models which are used to derive all models for testing. Our non-ignorable non-response models are 'close' to the ignorable non-response models, thereby reducing the effects of the assumptions about non-respondents that cannot be tested in non-response models. We have data from 35 counties, small areas, and therefore our models are hierarchical, a feature that allows a 'borrowing of strength' across the counties, and they provide a substantial reduction in variation. The non-ignorable non-response models are generalizations of the ignorable non-response models, and therefore, the non-ignorable non-response models allow broader inference. The joint posterior density of the parameters for each model is complex, and therefore, we fit each model using Markov chain Monte Carlo methods to obtain samples which are used to make inference about BMD and age. For each county we can estimate the proportion of individuals in each BMD and age cell of the categorical table, and we can assess the relation between BMD and age using the Bayes factor. A sensitivity analysis shows that there are differences (typically small) in inference that permits different levels of association between BMD and age. A simulation study shows that there is not much difference between the baseline ignorable and non-ignorable non-response models.
journal_name
Stat Medjournal_title
Statistics in medicineauthors
Nandram B,Liu N,Choi JW,Cox Ldoi
10.1002/sim.1985subject
Has Abstractpub_date
2005-04-15 00:00:00pages
1047-74issue
7eissn
0277-6715issn
1097-0258journal_volume
24pub_type
杂志文章abstract::Delay in the outcome variable is challenging for outcome-adaptive randomization, as it creates a lag between the number of subjects accrued and the information known at the time of the analysis. Motivated by a real-life pediatric ulcerative colitis trial, we consider a case where a short-term predictor is available fo...
journal_title:Statistics in medicine
pub_type: 杂志文章
doi:10.1002/sim.6222
更新日期:2014-10-15 00:00:00
abstract::The primary purpose of a disease surveillance system is to provide data for the detection of changes in the incidence of the disease. Methods for the analysis of data from surveillance systems are reviewed. A new procedure is proposed for use when the system includes geographically dispersed reporting units, such as h...
journal_title:Statistics in medicine
pub_type: 杂志文章
doi:10.1002/sim.4780080306
更新日期:1989-03-01 00:00:00
abstract::Genetic markers can be used as instrumental variables, in an analogous way to randomization in a clinical trial, to estimate the causal relationship between a phenotype and an outcome variable. Our purpose is to extend the existing methods for such Mendelian randomization studies to the context of multiple genetic mar...
journal_title:Statistics in medicine
pub_type: 杂志文章
doi:10.1002/sim.3843
更新日期:2010-05-30 00:00:00
abstract::We analyse the effect of using prevalence rates based on populations with different sizes in the power of spatial independence tests. We compare the well known spatial correlation Moran's index to three indexes obtained after adjusting for population density, one proposed by Oden, another proposed by Waldhör, and a th...
journal_title:Statistics in medicine
pub_type: 杂志文章
doi:10.1002/(sici)1097-0258(19990830)18:16<2147::aid-s
更新日期:1999-08-30 00:00:00
abstract::Among subjects who have experienced a biological event, such as menarche, menopause or a delivery, one cannot distinguish the effects of time since the event from age at the event due to the linear dependency among these time variables and age at study ('current age'). This is a well-known problem that also exists in ...
journal_title:Statistics in medicine
pub_type: 杂志文章
doi:10.1002/(SICI)1097-0258(19960730)15:14<1545::AID-S
更新日期:1996-07-30 00:00:00
abstract::Clustered grouped survival data arise naturally in clinical medicine and biological research. For example, in a randomized clinical trial, the variable of interest is the time to occurrence of a certain event with or without a new treatment and the data are collected from possibly correlated subjects from independent ...
journal_title:Statistics in medicine
pub_type: 杂志文章
doi:10.1002/sim.1323
更新日期:2003-06-30 00:00:00
abstract::A survey is conducted at w of K selection units or lists, e.g. health care institutions or weeks in a year, to estimate N, the total number of individuals with particular characteristics. Our estimator utilizes two items determined for each survey participant: the number, u, among the w lists in S and the number, j, a...
journal_title:Statistics in medicine
pub_type: 杂志文章
doi:10.1002/sim.3614
更新日期:2009-07-30 00:00:00
abstract::A new, intuitive method has recently been proposed to explore treatment-covariate interactions in survival data arising from two treatment arms of a clinical trial. The method is based on constructing overlapping subpopulations of patients with respect to one (or more) covariates of interest and in observing the patte...
journal_title:Statistics in medicine
pub_type: 杂志文章
doi:10.1002/sim.3524
更新日期:2009-04-15 00:00:00
abstract::Recurrent event data are commonly encountered in health-related longitudinal studies. In this paper time-to-events models for recurrent event data are studied with non-informative and informative censorings. In statistical literature, the risk set methods have been confirmed to serve as an appropriate and efficient ap...
journal_title:Statistics in medicine
pub_type: 杂志文章
doi:10.1002/sim.1029
更新日期:2002-02-15 00:00:00
abstract::We present a new approach to training back-propagation artificial neural nets (BP-ANN) based on regularization and cross-validation and on initialization by a logistic regression (LR) model. The new approach is expected to produce a BP-ANN predictor at least as good as the LR-based one. We have applied the approach to...
journal_title:Statistics in medicine
pub_type: 杂志文章
doi:10.1002/sim.1107
更新日期:2002-05-15 00:00:00
abstract::In this work, we describe a two-stage sampling design to estimate the infection prevalence in a population. In the first stage, an imperfect diagnostic test was performed on a random sample of the population. In the second stage, a different imperfect test was performed in a stratified random sample of the first sampl...
journal_title:Statistics in medicine
pub_type: 杂志文章
doi:10.1002/sim.6545
更新日期:2015-11-10 00:00:00
abstract::We have developed a method to longitudinally classify subjects into two or more prognostic groups using longitudinally observed values of markers related to the prognosis. We assume the availability of a training data set where the subjects' allocation into the prognostic group is known. The proposed method proceeds i...
journal_title:Statistics in medicine
pub_type: 杂志文章
doi:10.1002/sim.3849
更新日期:2010-12-30 00:00:00
abstract::We point out that the conventional methods for ties correction may be seriously biased when censoring times depend on covariates. A simple modification to the Efron correction method is suggested which works remarkably well in simulation studies. The method corresponds closely to breaking ties by random ordering. The ...
journal_title:Statistics in medicine
pub_type: 杂志文章
doi:10.1002/sim.2173
更新日期:2005-10-30 00:00:00
abstract::The use of the continual reassessment method (CRM) and other model-based approaches to design Phase I clinical trials has increased owing to the ability of the CRM to identify the maximum tolerated dose better than the 3 + 3 method. However, the CRM can be sensitive to the variance selected for the prior distribution ...
journal_title:Statistics in medicine
pub_type: 杂志文章
doi:10.1002/sim.5621
更新日期:2013-06-15 00:00:00
abstract::This paper investigates the design and analysis of dose-finding trials with two agents. The set of doses for each agent is fixed in advance. The goal of the trial is to find the set of dose combinations with probability of toxicity closest to a pre-specified value. For each of the two agents we assume that the probabi...
journal_title:Statistics in medicine
pub_type: 杂志文章
doi:10.1002/sim.1796
更新日期:2004-06-30 00:00:00
abstract::When interpreting screening mammograms radiologists decide whether suspicious abnormalities exist that warrant the recall of the patient for further testing. Previous work has found significant differences in interpretation among radiologists; their false-positive and false-negative rates have been shown to vary widel...
journal_title:Statistics in medicine
pub_type: 杂志文章
doi:10.1002/sim.2633
更新日期:2007-03-30 00:00:00
abstract::Case-control studies are prone to low power for testing gene-environment interactions (GXE) given the need for a sufficient number of individuals on each strata of disease, gene, and environment. We propose a new study design to increase power by strategically pooling biospecimens. Pooling biospecimens allows us to in...
journal_title:Statistics in medicine
pub_type: 杂志文章
doi:10.1002/sim.5357
更新日期:2012-11-20 00:00:00
abstract::With the increasing availability of detailed clinical information, there is optimism that treatment choices can be selectively directed to those individuals most likely to benefit. While standard clinical trials can establish whether a treatment appears to be effective on average, subsequent work is needed to determin...
journal_title:Statistics in medicine
pub_type: 杂志文章
doi:10.1002/sim.6138
更新日期:2014-07-30 00:00:00
abstract::Clinical trials, especially the randomized clinical trial, have been and will remain the gold standard for the evaluation of new interventions, including pharmaceuticals, biologics, medical devices, procedures, or behavioral modifications. Despite more than five decades of experience, there are still challenges in the...
journal_title:Statistics in medicine
pub_type: 杂志文章
doi:10.1002/sim.5405
更新日期:2012-11-10 00:00:00
abstract::Most statistical methodology for phase III clinical trials focuses on the comparison of a single experimental treatment with a control. An increasing desire to reduce the time before regulatory approval of a new drug is sought has led to development of two-stage or sequential designs for trials that combine the defini...
journal_title:Statistics in medicine
pub_type: 杂志文章
doi:10.1002/sim.1362
更新日期:2003-03-15 00:00:00
abstract::One may encounter the application of the two independent samples t-test to ordinal scaled data (for example, data that assume only the values 0, 1, 2, 3) from small samples. This situation clearly violates the underlying normality assumption for the t-test and one cannot appeal to large sample theory for validity. In ...
journal_title:Statistics in medicine
pub_type: 杂志文章
doi:10.1002/sim.4780060110
更新日期:1987-01-01 00:00:00
abstract::Non-linear mixed-effects models (NLMEMs) are used to improve information gathering from longitudinal studies and are applied to treatment evaluation in disease-evolution studies, such as human immunodeficiency virus (HIV) infection. The estimation of parameters and the statistical tests are critical issues in NLMEMs s...
journal_title:Statistics in medicine
pub_type: 杂志文章
doi:10.1002/sim.2950
更新日期:2007-11-30 00:00:00
abstract::This paper discusses and compares several estimators of mean rate of change in unbalanced longitudinal data based on a model with randomly distributed regression coefficients across individuals. The estimators are unweighted and weighted means of these coefficients. The paper also evaluates commonly used variance esti...
journal_title:Statistics in medicine
pub_type: 杂志文章
doi:10.1002/sim.4780060509
更新日期:1987-07-01 00:00:00
abstract::Typical analyses of lifetime data treat the time to death or failure as the response variable and use a variety of modelling strategies such as proportional hazards or fully parametric, to investigate the relationship between the response and covariates. In certain circumstances it may be more natural to view the dist...
journal_title:Statistics in medicine
pub_type: 杂志文章
doi:10.1002/sim.822
更新日期:2001-07-15 00:00:00
abstract::Screening and diagnostic tests are important in disease prevention or control. The predictive values of positive and negative (PPV and NPV) test results are two of four operational characteristics of a screening test. We review an existing method based on the generalized estimating equation (GEE) methodology for compa...
journal_title:Statistics in medicine
pub_type: 杂志文章
doi:10.1002/sim.2332
更新日期:2006-07-15 00:00:00
abstract::A relationship between baseline risk and treatment effect is increasingly investigated as a possible explanation of between-study heterogeneity in clinical trial meta-analysis. An approach that is still often applied in the medical literature is to plot the estimated treatment effects against the estimated measures of...
journal_title:Statistics in medicine
pub_type: 杂志文章
doi:10.1002/1097-0258(20001230)19:24<3497::aid-sim830>
更新日期:2000-12-30 00:00:00
abstract::In longitudinal studies, missing observations occur commonly. It has been well known that biased results could be produced if missingness is not properly handled in the analysis. Authors have developed many methods with the focus on either incomplete response or missing covariate observations, but rarely on both. The ...
journal_title:Statistics in medicine
pub_type: 杂志文章
doi:10.1002/sim.5536
更新日期:2013-02-28 00:00:00
abstract::It is often of interest to use observational data to estimate the causal effect of a target exposure or treatment on an outcome. When estimating the treatment effect, it is essential to appropriately adjust for selection bias due to observed confounders using, for example, propensity score weighting. Selection bias du...
journal_title:Statistics in medicine
pub_type: 杂志文章
doi:10.1002/sim.8549
更新日期:2020-08-15 00:00:00
abstract::Correlated data are obtained in longitudinal epidemiological studies, where repeated measurements are taken on individuals or groups over time. Such longitudinal data are ideally analyzed using multilevel modeling approaches, which appropriately account for the correlations in repeated responses in the same individual...
journal_title:Statistics in medicine
pub_type: 杂志文章
doi:10.1002/sim.5880
更新日期:2013-12-10 00:00:00
abstract::Genetic networks for gene expression data are often built by graphical models, which in turn are built from pair-wise correlations of gene expression levels. A key feature of building graphical models is the evaluation of conditional independence of two traits, given other traits. When conditional independence can be ...
journal_title:Statistics in medicine
pub_type: 杂志文章
doi:10.1002/sim.3274
更新日期:2008-08-30 00:00:00