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Meta-Analysis of Diagnostic Test Accuracy Studies with Multiple Thresholds using Survival MethodsEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
This article concerns the situation where multiple studies have evaluated the same diagnostic test with the same multiple thresholds in a population of non-diseased and diseased individuals. Recently, bivariate meta-analysis has been proposed for the pooling of sensitivity and specificity, which are likely to be negatively correlated within studies. These ideas have been extended to the situation of diagnostic tests with multiple thresholds, leading to a multinomial model with multivariate normal between-study variation. This approach is efficient, but computer-intensive and its convergence is highly dependent on starting ...
Source: Biometrical Journal - November 19, 2009 Category: Biotechnology Authors: H. Putter, M. Fiocco, T. Stijnen Source Type: journals

Minimum-Norm Estimation for Binormal Receiver Operating Characteristic (ROC) CurvesEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
We present a new method to estimate the parameters of a popular semi-parametric ROC model, called the binormal model. Our method is based on minimization of the functional distance between two estimators of an unknown transformation postulated by the model, and has a simple, closed-form solution. We study the asymptotics of our estimators, show via simulation that they compare favorably with existing estimators, and illustrate how covariates may be incorporated into the norm minimization framework. (Source: Biometrical Journal)
Source: Biometrical Journal - November 6, 2009 Category: Biotechnology Authors: Ori Davidov, Yuval Nov Source Type: journals

Generalized Confidence Intervals for Ratios of Regression Coefficients with Applications to BioassaysEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The problem of constructing a confidence interval for the ratio of two regression coefficients is addressed in the context of multiple regression. The concept of a Generalized Confidence Interval is used, and the resulting confidence interval is shown to perform well in terms of coverage probability. The proposed methodology always results in an interval, unlike the confidence region generated from Fieller's theorem. The procedure can easily be implemented for parallel-line assays, slope-ratio assays, and quantal assays under a probit model. Furthermore, this approach can also be extended to compute confidence intervals ba...
Source: Biometrical Journal - November 5, 2009 Category: Biotechnology Authors: Ionut Bebu, Françoise Seillier-Moiseiwitsch, Thomas Mathew Source Type: journals

Homogeneity/Heterogeneity Hypotheses for Standardized Mortality Ratios Based on Minimum Power-divergence EstimatorsEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
This paper analyzes the power divergence estimators when homogeneity/heterogeneity hypotheses among standardized mortality ratios (SMRs) are taken into account. A Monte Carlo study shows that when the standard mortality rate is not external, that is it is estimated from the sample data, these estimators have a good performance even for small sample sets and in particular the minimum chi-square estimators have a better behavior compared to the classical maximum likelihood estimators. In order to make decisions under homogeneity/heterogeneity hypotheses of SMRs we propose some test-statistics which consider the minimum power...
Source: Biometrical Journal - October 12, 2009 Category: Biotechnology Authors: Leandro Pardo, Nirian Martín Source Type: journals

Estimating Antihypertensive Effects of Combination Therapy in an Observational Study Using Marginal Structural ModelsEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The evaluation of the antihypertensive effect of multiple antihypertensive drugs using data from an observational study requires adjustment for time-dependent confounders. Marginal structural models (MSMs) have been proposed to address this type of confounding through inverse probability weighting. Generally, the probabilities are estimated using logistic regression models that assume linearity between the logistic link and the predictors, but the linearity might be inaccurate. In this article, we proposed MSMs to assess the blood pressure-lowering effects of combination therapy with olmesartan medoxomil (OLM) plus calcium...
Source: Biometrical Journal - October 12, 2009 Category: Biotechnology Authors: Masahiro Sugihara, Toshio Kushiro, Ikuo Saito, Yasuyuki Matsushita, Katsutoshi Hiramatsu Source Type: journals

Neighborhood Dependence in Bayesian Spatial ModelsEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
This article clarifies many of these puzzling results. We show that the neighborhood graph structure, synthesized in eigenvalues and eigenvectors structure of a matrix associated with the adjacency matrix, determines most of the apparently anomalous behavior. We illustrate our conclusions with regular and irregular lattices including lines, grids, and lattices based on real maps. (Source: Biometrical Journal)
Source: Biometrical Journal - October 12, 2009 Category: Biotechnology Authors: Renato Assunção, Elias Krainski Source Type: journals

Correction: A Stochastic Regression Model for General Trend Analysis of Longitudinal Continuous Data. Biometrical Journal 2009; 51, 571-587Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
No Abstract (Source: Biometrical Journal)
Source: Biometrical Journal - October 8, 2009 Category: Biotechnology Authors: Wei-Hsiung Chao, Su-Hua Chen Source Type: journals

Adaptive Design Methods in Clinical Trials. Chow, S. C. and Chang, M. (2007). Boca Raton, FL, USA: Chapman & Hall/CRC. ISBN 13: 978-1-58488-776-8Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
No Abstract (Source: Biometrical Journal)
Source: Biometrical Journal - October 8, 2009 Category: Biotechnology Authors: Guido Knapp Source Type: journals

Risk Factor Adjustment in Marginal Structural Model Estimation of Optimal Treatment RegimesEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Marginal structural models (MSMs) are an increasingly popular tool, particularly in epidemiological applications, to handle the problem of time-varying confounding by intermediate variables when studying the effect of sequences of exposures. Considerable attention has been devoted to the optimal choice of treatment model for propensity score-based methods and, more recently, to variable selection in the treatment model for inverse weighting in MSMs. However, little attention has been paid to the modeling of the outcome of interest, particularly with respect to the best use of purely predictive, non-confounding variables in...
Source: Biometrical Journal - October 7, 2009 Category: Biotechnology Authors: Erica E. M. Moodie Source Type: journals

Statistical Tests Based on New Composite Hypotheses in Clinical Trials Reflecting the Relative Clinical Importance of Multiple Endpoints QuantitativelyEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
In clinical trials, several endpoints (EPs) are often evaluated to compare treatments in some therapeutic area. Suppose that there are two EPs in a clinical trial. We propose a new set of composite hypotheses for continuous variables, taking the relative clinical importance of the EPs into account. The main hypotheses were formulated to show that a treatment is so superior to the control treatment, which is not necessarily a placebo, in one EP, that the possible non-inferiority of the treatment by at most a certain value in the other EP can be compensated sufficiently, taking the clinical point of view into account. The ma...
Source: Biometrical Journal - September 22, 2009 Category: Biotechnology Authors: Masako Nishikawa, Toshiro Tango, Megu Ohtaki Source Type: journals

"Assessment of Multiple Ordinal Endpoints" by L. Häberle, A. Pfahlberg and O. Gefeller Biometrical Journal (2009) 51, 217-226 Article: . Authors' reply:Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
No Abstract (Source: Biometrical Journal)
Source: Biometrical Journal - September 20, 2009 Category: Biotechnology Authors: Knut M. Wittkowski Source Type: journals

Spatial Cluster Detection for Repeatedly Measured Outcomes while Accounting for Residential HistoryEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Spatial cluster detection has become an important methodology in quantifying the effect of hazardous exposures. Previous methods have focused on cross-sectional outcomes that are binary or continuous. There are virtually no spatial cluster detection methods proposed for longitudinal outcomes. This paper proposes a new spatial cluster detection method for repeated outcomes using cumulative geographic residuals. A major advantage of this method is its ability to readily incorporate information on study participants relocation, which most cluster detection statistics cannot. Application of these methods will be illustrated by...
Source: Biometrical Journal - September 15, 2009 Category: Biotechnology Authors: Andrea J. Cook, Diane R. Gold, Yi Li Source Type: journals

Response Adaptive Designs with a Variance-penalized CriterionEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
We consider a response adaptive design of clinical trials with a variance-penalized criterion. It is shown that this criterion evaluates the performance of a response adaptive design based on both the number of patients assigned to the better treatment and the power of the statistical test. A new proportion of treatment allocation is proposed and the doubly biased coin procedure is used to target the proposed proportion. Under reasonable assumptions, the proposed design is demonstrated to generate an asymptotic variance of allocation proportions, which is smaller than that of the drop-the-loser design. Simulation compariso...
Source: Biometrical Journal - September 14, 2009 Category: Biotechnology Authors: Yanqing Yi, Xikui Wang Source Type: journals

Authors' replyEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
No Abstract (Source: Biometrical Journal)
Source: Biometrical Journal - August 22, 2009 Category: Biotechnology Authors: Lothar Häberle, Annette Pfahlberg, Olaf Gefeller Source Type: journals

Mathematics of Shape Description. A Morphological Approach to Image Processing and Computer Graphics. P. K. Ghosh and K. Deguchi (2008). Singapore: J. Wiley (Asia). ISBN: 978-0-470-82307-1Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
No Abstract (Source: Biometrical Journal)
Source: Biometrical Journal - August 20, 2009 Category: Biotechnology Authors: Dietrich Stoyan Source Type: journals

Multivariable Model-building. P. Royston and W. Sauerbrei (2008). New York: Wiley. ISBN: 978-0-470-02842-1Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
No Abstract (Source: Biometrical Journal)
Source: Biometrical Journal - August 20, 2009 Category: Biotechnology Authors: Ralf Bender, Ulrich Grouven Source Type: journals

Joint Estimation of Diagnostic Accuracy Measures for Paired Organs - Application in OphthalmologyEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Diagnostic studies in ophthalmology frequently involve binocular data where pairs of eyes are evaluated, through some diagnostic procedure, for the presence of certain diseases or pathologies. The simplest approach of estimating measures of diagnostic accuracy, such as sensitivity and specificity, treats eyes as independent, consequently yielding incorrect estimates, especially of the standard errors. Approaches that account for the inter-eye correlation include regression methods using generalized estimating equations and likelihood techniques based on various correlated binomial models. The paper proposes a simple altern...
Source: Biometrical Journal - August 20, 2009 Category: Biotechnology Authors: Alexander R. de Leon, Andrea Soo, Daniel C. Bonzo, Christopher J. Rudnisky Source Type: journals

Haplotype Inference for Population Data with Genotyping ErrorsEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Inference of haplotypes is important in genetic epidemiology studies. However, all large genotype data sets have errors due to the use of inexpensive genotyping machines that are fallible and shortcomings in genotyping scoring softwares, which can have an enormous impact on haplotype inference. In this article, we propose two novel strategies to reduce the impact induced by genotyping errors in haplotype inference. The first method makes use of double sampling. For each individual, the "GenoSpectrum" that consists of all possible genotypes and their corresponding likelihoods are computed. The second method is a genotype cl...
Source: Biometrical Journal - August 16, 2009 Category: Biotechnology Authors: Wensheng Zhu, Anthony Y. C. Kuk, Jianhua Guo Tags: Research Articles Source Type: journals

On the Impact of Parametric Assumptions and Robust Alternatives for Longitudinal Data AnalysisEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Models for longitudinal data are employed in a wide range of behavioral, biomedical, psychosocial, and health-care-related research. One popular model for continuous response is the linear mixed-effects model (LMM). Although simulations by recent studies show that LMM provides reliable estimates under departures from the normality assumption for complete data, the invariable occurrence of missing data in practical studies renders such robustness results less useful when applied to real study data. In this paper, we show by simulated studies that in the presence of missing data estimates of the fixed effect of LMM are biase...
Source: Biometrical Journal - August 16, 2009 Category: Biotechnology Authors: Naiji Lu, Wan Tang, Hua He, Qin Yu, Paul Crits-Christoph, Hui Zhang, Xin Tu Tags: Research Articles Source Type: journals

Classification of Therapy Resistance Based on Longitudinal Biomarker ProfilesEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
To classify patients either as resistant or non-resistant to HIV therapy based on longitudinal viral load profiles, we applied longitudinal quadratic discriminant analysis and examined various measures, mainly derived from the Brier Score, to assess the biomarker performance in terms of discrimination and calibration. The analysis of the application data revealed an increase in performance by using longer profiles instead of single biomarker measurements. Simulations showed that the selection of mixed models for the estimation of the group-specific discriminant rule parameters should be based on BIC, rather than on the bes...
Source: Biometrical Journal - August 16, 2009 Category: Biotechnology Authors: Mareike Kohlmann, Leonhard Held, Veit Peter Grunert Tags: Research Articles Source Type: journals

Alternative Confidence Regions for Bonferroni-Based Closed-Testing Procedures that are not Alpha-ExhaustiveEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
This article complements the results in Guilbaud (Biometrical Journal 2008; 50:678-692). Simultaneous confidence regions were derived in that article that correspond to any given multiple testing procedure (MTP) in a fairly large class of consonant closed-testing procedures based on marginal p-values and weighted Bonferroni tests for intersection hypotheses. This class includes Holm's MTP, the fixed-sequence MTP, gatekeeping MTPs, fallback MTPs, multi-stage fallback MTPs, and recently proposed MTPs specified through a graphical representation and associated rejection algorithm. More general confidence regions are proposed ...
Source: Biometrical Journal - August 3, 2009 Category: Biotechnology Authors: Olivier Guilbaud Source Type: journals

A Stochastic Regression Model for General Trend Analysis of Longitudinal Continuous DataEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
A predictive continuous time model is developed for continuous panel data to assess the effect of time-varying covariates on the general direction of the movement of a continuous response that fluctuates over time. This is accomplished by reparameterizing the infinitesimal mean of an Ornstein-Uhlenbeck processes in terms of its equilibrium mean and a drift parameter, which assesses the rate that the process reverts to its equilibrium mean. The equilibrium mean is modeled as a linear predictor of covariates. This model can be viewed as a continuous time first-order autoregressive regression model with time-varying lag effec...
Source: Biometrical Journal - August 3, 2009 Category: Biotechnology Authors: Wei-Hsiung Chao, Su-Hua Chen Source Type: journals

Letter to the EditorEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
No Abstract (Source: Biometrical Journal)
Source: Biometrical Journal - August 3, 2009 Category: Biotechnology Authors: F. J. Rubio, S. Pérez-Elizalde Source Type: journals

Biometrical Journal and Reproducible ResearchEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
No Abstract (Source: Biometrical Journal)
Source: Biometrical Journal - July 31, 2009 Category: Biotechnology Authors: Torsten Hothorn, Leonhard Held, Tim Friede Tags: Editorial Source Type: journals

Modeling Infectious Diseases in Humans and Animals. M. J. Keeling and P. Rohani (2008). NJ, USA: Princeton University Press. ISBN: 978-0-691-11617-3Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
No Abstract (Source: Biometrical Journal)
Source: Biometrical Journal - July 31, 2009 Category: Biotechnology Authors: Michael Höhle Source Type: journals

A Non-parametric Conditional Bivariate Reference Region with an Application to Height/Weight Measurements on Normal GirlsEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
A conceptually simple two-dimensional conditional reference curve is described. The curve gives a decision basis for determining whether a bivariate response from an individual is "normal" or "abnormal" when taking into account that a third (conditioning) variable may influence the bivariate response. The reference curve is not only characterized analytically but also by geometric properties that are easily communicated to medical doctors - the users of such curves. The reference curve estimator is completely non-parametric, so no distributional assumptions are needed about the two-dimensional response. An example that wil...
Source: Biometrical Journal - July 30, 2009 Category: Biotechnology Authors: Jorgen Holm Petersen Source Type: journals

A New Approach for Handling Longitudinal Count Data with Zero-Inflation and Overdispersion: Poisson Geometric Process ModelEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
For time series of count data, correlated measurements, clustering as well as excessive zeros occur simultaneously in biomedical applications. Ignoring such effects might contribute to misleading treatment outcomes. A generalized mixture Poisson geometric process (GMPGP) model and a zero-altered mixture Poisson geometric process (ZMPGP) model are developed from the geometric process model, which was originally developed for modelling positive continuous data and was extended to handle count data. These models are motivated by evaluating the trend development of new tumour counts for bladder cancer patients as well as by id...
Source: Biometrical Journal - July 30, 2009 Category: Biotechnology Authors: Wai-Yin Wan, Jennifer S. K. Chan Source Type: journals

The Sign of the Unmeasured Confounding Bias under Various Standard PopulationsEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Unmeasured confounders are a common problem in drawing causal inferences in observational studies. VanderWeele (Biometrics 2008, 64, 702-706) presented a theorem that allows researchers to determine the sign of the unmeasured confounding bias when monotonic relationships hold between the unmeasured confounder and the treatment, and between the unmeasured confounder and the outcome. He showed that his theorem can be applied to causal effects with the total group as the standard population, but he did not mention the causal effects with treated and untreated groups as the standard population. Here, we extend his results to t...
Source: Biometrical Journal - July 30, 2009 Category: Biotechnology Authors: Yasutaka Chiba Source Type: journals

Order-restricted Scores Test for the Evaluation of Population-based Case-control Studies when the Genetic Model is UnknownEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The Cochran-Armitage (CA) linear trend test for proportions is often used for genotype-based analysis of candidate gene association. Depending on the underlying genetic mode of inheritance, the use of model-specific scores maximises the power. Commonly, the underlying genetic model, i.e. additive, dominant or recessive mode of inheritance, is a priori unknown. Association studies are commonly analysed using permutation tests, where both inference and identification of the underlying mode of inheritance are important. Especially interesting are tests for case-control studies, defined by a maximum over a series of standardis...
Source: Biometrical Journal - July 30, 2009 Category: Biotechnology Authors: Ludwig A. Hothorn, Torsten Hothorn Source Type: journals

Interpreting Statistical Evidence with Empirical Likelihood FunctionsEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
This article discusses the use of empirical likelihood functions, a well-developed methodology in the frequentist paradigm, to interpret statistical evidence in nonparametric and semiparametric situations. A comparative review of literature shows that, while an empirical likelihood is not a true probability density, it has the essential properties, namely consistency and local asymptotic normality that unify and justify the various parametric likelihood methods for evidential analysis. Real examples are presented to illustrate and compare the empirical likelihood method and the parametric likelihood methods. These methods ...
Source: Biometrical Journal - July 30, 2009 Category: Biotechnology Authors: Zhiwei Zhang Source Type: journals

A Generalized Log-Rank-Type Test for Comparing Survivals with Doubly Interval-Censored DataEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
In doubly interval-censored data, the survival time of interest is defined as the elapsed time between an initial event and a subsequent event, but the occurrences of both events cannot be observed exactly. Instead, only right- or interval-censored observations on the occurrence times are available. Our purpose is to develop a generalized log-rank-type test for comparing survival functions of several groups. For the same problem, Sun (The Statistical Analysis of Interval-censored Failure Time Data, Springer, New York) suggested a nonparametric test based on the estimated marginal survival functions of the two related event...
Source: Biometrical Journal - July 30, 2009 Category: Biotechnology Authors: Jinheum Kim, Yang-Jin Kim, Chung Mo Nam Source Type: journals

Rounding Strategies for Multiply Imputed Binary DataEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Multiple imputation (MI) has emerged in the last two decades as a frequently used approach in dealing with incomplete data. Gaussian and log-linear imputation models are fairly straightforward to implement for continuous and discrete data, respectively. However, in missing data settings that include a mix of continuous and discrete variables, the lack of flexible models for the joint distribution of different types of variables can make the specification of the imputation model a daunting task. The widespread availability of software packages that are capable of carrying out MI under the assumption of joint multivariate no...
Source: Biometrical Journal - July 30, 2009 Category: Biotechnology Authors: Hakan Demirtas Source Type: journals

Sampling techniques for forest inventories. D. Mandallaz (2008). Boca Raton: Chapman & Hall/CRC. ISBN: 978-1-584-88976-2Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
No Abstract (Source: Biometrical Journal)
Source: Biometrical Journal - July 30, 2009 Category: Biotechnology Authors: Dietrich Stoyan Source Type: journals

Ecological Models and Data in R. B. M. Bolker (2008). Princeton, NJ, USA: Princeton University Press. ISBN 978-0-691-12522-0Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
No Abstract (Source: Biometrical Journal)
Source: Biometrical Journal - July 30, 2009 Category: Biotechnology Authors: Martin Schlather Source Type: journals

Applied Survival Analysis (2nd Edn.). D. Hosmer, S. Lemeshow, and S. May (2008). Hoboken: Wiley Series in Probability and Statistics. ISBN: 978-0-471-75499-2Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
No Abstract (Source: Biometrical Journal)
Source: Biometrical Journal - July 30, 2009 Category: Biotechnology Authors: Jan Beyersmann Source Type: journals

Bayesian analysis for nonlinear regression model under skewed errors, with application in growth curvesEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
We have considered a Bayesian approach for the nonlinear regression model by replacing the normal distribution on the error term by some skewed distributions, which account for both skewness and heavy tails or skewness alone. The type of data considered in this paper concerns repeated measurements taken in time on a set of individuals. Such multiple observations on the same individual generally produce serially correlated outcomes. Thus, additionally, our model does allow for a correlation between observations made from the same individual. We have illustrated the procedure using a data set to study the growth curves of a ...
Source: Biometrical Journal - July 22, 2009 Category: Biotechnology Authors: Rolando De la Cruz, Márcia D. Branco Source Type: journals

Datenanalyse mit STATA. U. Kohler and F. Kreuter (2008). Munich: Oldenbourg Wissenschaftsverlag. ISBN: 978-3-486-58456-1Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
No Abstract (Source: Biometrical Journal)
Source: Biometrical Journal - July 7, 2009 Category: Biotechnology Authors: Milo A. Puhan Tags: Book Reviews Source Type: journals

Highest Density Difference Region Estimation with Application to Flow Cytometric DataEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Motivated by the needs of scientists using flow cytometry, we study the problem of estimating the region where two multivariate samples differ in density. We call this problem highest density difference region estimation and recognise it as a two-sample analogue of highest density region or excess set estimation. Flow cytometry samples are typically in the order of 10 000 and 100 000 and with dimension ranging from about 3 to 20. The industry standard for the problem being studied is called Frequency Difference Gating, due to Roederer and Hardy (). After couching the problem in a formal statistical framework we devise an a...
Source: Biometrical Journal - July 7, 2009 Category: Biotechnology Authors: Tarn Duong, Inge Koch, M. P. Wand Tags: Research Articles Source Type: journals

Estimation of the ROC Curve under Verification BiasEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The ROC (receiver operating characteristic) curve is the most commonly used statistical tool for describing the discriminatory accuracy of a diagnostic test. Classical estimation of the ROC curve relies on data from a simple random sample from the target population. In practice, estimation is often complicated due to not all subjects undergoing a definitive assessment of disease status (verification). Estimation of the ROC curve based on data only from subjects with verified disease status may be badly biased. In this work we investigate the properties of the doubly robust (DR) method for estimating the ROC curve under ver...
Source: Biometrical Journal - July 7, 2009 Category: Biotechnology Authors: Ronen Fluss, Benjamin Reiser, David Faraggi, Andrea Rotnitzky Tags: Research Articles Source Type: journals

The Concordance Index C and the Mann-Whitney Parameter Pr(X>Y) with Randomly Censored DataEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Harrell's c-index or concordance C has been widely used as a measure of separation of two survival distributions. In the absence of censored data, the c-index estimates the Mann-Whitney parameter Pr(X>Y), which has been repeatedly utilized in various statistical contexts. In the presence of randomly censored data, the c-index no longer estimates Pr(X>Y); rather, a parameter that involves the underlying censoring distributions. This is in contrast to Efron's maximum likelihood estimator of the Mann-Whitney parameter, which is recommended in the setting of random censorship. (Source: Biometrical Journal)
Source: Biometrical Journal - July 7, 2009 Category: Biotechnology Authors: James A. Koziol, Zhenyu Jia Tags: Short Communication Source Type: journals

Multilevel Mixture Cure Models with Random EffectsEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
This paper extends the multilevel survival model by allowing the existence of cured fraction in the model. Random effects induced by the multilevel clustering structure are specified in the linear predictors in both hazard function and cured probability parts. Adopting the generalized linear mixed model (GLMM) approach to formulate the problem, parameter estimation is achieved by maximizing a best linear unbiased prediction (BLUP) type log-likelihood at the initial step of estimation, and is then extended to obtain residual maximum likelihood (REML) estimators of the variance component. The proposed multilevel mixture cure...
Source: Biometrical Journal - July 7, 2009 Category: Biotechnology Authors: Xin Lai, Kelvin K. W. Yau Tags: Research Articles Source Type: journals

Complementary Log-Log Regression for the Estimation of Covariate-Adjusted Prevalence Ratios in the Analysis of Data from Cross-Sectional StudiesEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
We assessed complementary log-log (CLL) regression as an alternative statistical model for estimating multivariable-adjusted prevalence ratios (PR) and their confidence intervals. Using the delta method, we derived an expression for approximating the variance of the PR estimated using CLL regression. Then, using simulated data, we examined the performance of CLL regression in terms of the accuracy of the PR estimates, the width of the confidence intervals, and the empirical coverage probability, and compared it with results obtained from log-binomial regression and stratified Mantel-Haenszel analysis. Within the range of v...
Source: Biometrical Journal - July 7, 2009 Category: Biotechnology Authors: Alan D. Penman, William D. Johnson Tags: Research Articles Source Type: journals

Analysis of Misclassified Correlated Binary Data Using a Multivariate Probit Model when Covariates are Subject to Measurement ErrorEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
A multivariate probit model for correlated binary responses given the predictors of interest has been considered. Some of the responses are subject to classification errors and hence are not directly observable. Also measurements on some of the predictors are not available; instead the measurements on its surrogate are available. However, the conditional distribution of the unobservable predictors given the surrogate is completely specified. Models are proposed taking into account either or both of these sources of errors. Likelihood-based methodologies are proposed to fit these models. To ascertain the effect of ignoring ...
Source: Biometrical Journal - July 7, 2009 Category: Biotechnology Authors: Surupa Roy, Tathagata Banerjee Tags: Research Articles Source Type: journals

Modelling Tree Roots in Mixed Forest Stands by Inhomogeneous Marked Gibbs Point ProcessesEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The aim of the paper is to apply point processes to root data modelling. We propose a new approach to parametric inference when the data are inhomogeneous replicated marked point patterns. We generalize Geyer's saturation point process to a model, which combines inhomogeneity, marks and interaction between the marked points. Furthermore, the inhomogeneity influences the definition of the neighbourhood of points. Using the maximum pseudolikelihood method, this model is then fitted to root data from mixed stands of Norway spruce (Picea abies (L.) Karst.) and European beech (Fagus sylvatica L.) to quantify the degree of root ...
Source: Biometrical Journal - June 30, 2009 Category: Biotechnology Authors: Stefanie Eckel, Frank Fleischer, Pavel Grabarnik, Marian Kazda, Aila Särkkä, Volker Schmidt Source Type: journals

Comparing Accuracy in an Unpaired Post-market Device Study with Incomplete Disease AssessmentEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The sensitivity and specificity of a new medical device are often compared relative to that of an existing device by calculating ratios of sensitivities and specificities. Although it would be ideal for all study subjects to receive the gold standard so true disease status was known for all subjects, it is often not feasible or ethical to obtain disease status for everyone. This paper proposes two unpaired designs where each subject is only administered one of the devices and device results dictate which subjects are to receive disease verification. Estimators of the ratio of accuracy and corresponding confidence intervals...
Source: Biometrical Journal - June 30, 2009 Category: Biotechnology Authors: Todd A. Alonzo Source Type: journals

A Bayesian Long-term Survival Model Parametrized in the Cured FractionEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The main goal of this paper is to investigate a cure rate model that comprehends some well-known proposals found in the literature. In our work the number of competing causes of the event of interest follows the negative binomial distribution. The model is conveniently reparametrized through the cured fraction, which is then linked to covariates by means of the logistic link. We explore the use of Markov chain Monte Carlo methods to develop a Bayesian analysis in the proposed model. The procedure is illustrated with a numerical example. (Source: Biometrical Journal)
Source: Biometrical Journal - June 30, 2009 Category: Biotechnology Authors: Mário de Castro, Vicente G. Cancho, Josemar Rodrigues Source Type: journals

Obituary: Klaus BellmannEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
No Abstract (Source: Biometrical Journal)
Source: Biometrical Journal - June 24, 2009 Category: Biotechnology Authors: Ludwig A. Hothorn Source Type: journals

Household Epidemics: Modelling Effects of Early Stage VaccinationEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
A Markovian susceptible [rarr] infectious [rarr] removed (SIR) epidemic model is considered in a community partitioned into households. A vaccination strategy, which is implemented during the early stages of the disease following the detection of infected individuals is proposed. In this strategy, the detection occurs while an individual is infectious and other susceptible household members are vaccinated without further delay. Expressions are derived for the influence on the reproduction numbers of this vaccination strategy for equal and unequal household sizes. We fit previously estimated parameters from influenza and us...
Source: Biometrical Journal - June 21, 2009 Category: Biotechnology Authors: Nyimvua Shaban, Mikael Andersson, Åke Svensson, Tom Britton Source Type: journals

Elementary Bayesian Biostatistics. L. A. Moyé (2008). Boca Raton: Chapman & Hall/CRC. ISBN 978-1-58488-724-9Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
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Source: Biometrical Journal - June 5, 2009 Category: Biotechnology Authors: Arno Fritsch Source Type: journals

Measures of Disassortativeness and their Application to Directly Transmitted InfectionsEmail this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
We propose a measure of disassortativeness to summarize contact patterns relevant to the transmission of directly transmitted infections. We discuss the properties of this measure, describe standardization relative to homogeneous mixing, and generalize it to multivariate contact structures. We explore some of its properties and apply our methods to serological surveys of close contact infections and surveys of self-reported social contacts obtained in several European countries. (Source: Biometrical Journal)
Source: Biometrical Journal - June 2, 2009 Category: Biotechnology Authors: C. P. Farrington, H. J. Whitaker, J. Wallinga, P. Manfredi Source Type: journals