The ghosts of departed quantities: approaches to dealing with observations below the limit of quantitation.

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

authors： Wang W,Davis CS,Soong SJ

更新日期：2006-07-15 00:00:00

abstract：:Pattern-mixture models (PMM) and selection models (SM) are alternative approaches for statistical analysis when faced with incomplete data and a nonignorable missing-data mechanism. Both models make empirically unverifiable assumptions and need additional constraints to identify the parameters. Here, we first introduc...

journal_title：Statistics in medicine

authors： Kaciroti NA,Raghunathan T

更新日期：2014-11-30 00:00:00

abstract：:Motivated by a study about prompt coronary angiography in myocardial infarction, we propose a method to estimate the causal effect of a treatment in two-arm experimental studies with possible noncompliance in both treatment and control arms. We base the method on a causal model for repeated binary outcomes (before and...

journal_title：Statistics in medicine

authors： Bartolucci F,Farcomeni A

更新日期：2013-11-10 00:00:00

abstract：:Relative survival provides a measure of the proportion of patients dying from the disease under study without requiring the knowledge of the cause of death. We propose an overall strategy based on regression models to estimate the relative survival and model the effects of potential prognostic factors. The baseline ha...

journal_title：Statistics in medicine

authors： Remontet L,Bossard N,Belot A,Estève J,French network of cancer registries FRANCIM.

更新日期：2007-05-10 00:00:00

abstract：:Recent studies have indicated variation in the infectivity beta of HIV among heterosexual couples. We represent this heterogeneity by modelling beta as a random variable. Using data on the number of contacts and seroconversion of couples, we fit the model by maximum-likelihood estimation with a beta distribution and a...

journal_title：Statistics in medicine

authors： Wiley JA,Herschkorn SJ,Padian NS

更新日期：1989-01-01 00:00:00

abstract：:In this paper, we argue that causal effect models for realistic individualized treatment rules represent an attractive tool for analyzing sequentially randomized trials. Unlike a number of methods proposed previously, this approach does not rely on the assumption that intermediate outcomes are discrete or that models ...

journal_title：Statistics in medicine

authors： Bembom O,van der Laan MJ

更新日期：2008-08-30 00:00:00

abstract：:Equivalence trials aim to show that two treatments have equivalent therapeutic effects. The approach is to define, in advance, a range of equivalence -d to +d for the treatment difference such that any value in the range is clinically unimportant. If the confidence interval for the difference, calculated after the tri...

journal_title：Statistics in medicine

authors： Ebbutt AF,Frith L

更新日期：1998-08-15 00:00:00

abstract：:In any field in which decisions are subject to measurements, interchangeability between the methods used to obtain these measurements is essential. To consider methods as interchangeable, a certain degree of agreement is needed between the measurements they provide. The concordance correlation coefficient is an index ...

journal_title：Statistics in medicine

authors： Carrasco JL,Jover L

更新日期：2005-12-30 00:00:00

abstract：:For patients who were previously treated for prostate cancer, salvage hormone therapy is frequently given when the longitudinal marker prostate-specific antigen begins to rise during follow-up. Because the treatment is given by indication, estimating the effect of the hormone therapy is challenging. In a previous pape...

journal_title：Statistics in medicine

authors： Taylor JM,Shen J,Kennedy EH,Wang L,Schaubel DE

更新日期：2014-01-30 00:00:00

abstract：:Recently, Wu and Follmann developed summary measures to adjust for informative drop-out in longitudinal studies where drop-out depends on the underlying true value of the response. In this paper we evaluate these procedures in the common situation where drop-out depends on the observed responses. We also discuss vario...

journal_title：Statistics in medicine

authors： Wu MC,Albert PS,Wu BU

更新日期：2001-01-15 00:00:00

abstract：:Omitted variable bias is discussed in the context of linear models. It is shown that the effect of omitted variables can be controlled in linear models for metric dependent variables by using data from follow-up studies. Two different models for analysing such data are proposed. In the first model the omitted variable...

journal_title：Statistics in medicine

authors： Rehm J,Arminger G,Kohlmeier L

更新日期：1992-06-30 00:00:00

abstract：:In modern observational studies using electronic health records or other routinely collected data, both the outcome and covariates of interest can be error-prone and their errors often correlated. A cost-effective solution is the two-phase design, under which the error-prone outcome and covariates are observed for all...

journal_title：Statistics in medicine

authors： Tao R,Lotspeich SC,Amorim G,Shaw PA,Shepherd BE

更新日期：2021-02-10 00:00:00

abstract：:Comparative calibration is the broad statistical methodology used to assess the calibration of a set of p instruments, each designed to measure the same characteristic, on a common group of individuals. Different from the usual calibration problem, the true underlying quantity measured is unobservable. Many authors ha...

journal_title：Statistics in medicine

authors： Lu Y,Ye K,Mathur AK,Hui S,Fuerst TP,Genant HK

更新日期：1997-08-30 00:00:00

abstract：:In this paper we examine the efficiency of a generalization of the traditional normal linear (LDA) or quadratic (QDA) discriminant analysis. This procedure (the generalized discriminant analysis, GDA) replaces each normal density used in the traditional classification rule by a Fourier series density estimator which '...

journal_title：Statistics in medicine

authors： Odom-Maryon T,Langholz B,Niland J,Azen S

更新日期：1991-03-01 00:00:00

abstract：:The receiver operating characteristic (ROC) curve can be utilized to evaluate the performance of diagnostic tests. The area under the ROC curve (AUC) is a widely used summary index for comparing multiple ROC curves. Both parametric and nonparametric methods have been developed to estimate and compare the AUCs. However...

journal_title：Statistics in medicine

authors： Yao W,Li Z,Graubard BI

更新日期：2015-04-15 00:00:00

abstract：:This paper presents a statistical analysis of treatment effects in 24-hour ambulatory blood pressure recordings. The statistical models account for circadian rhythms, subject effects, and the effects of treatment with drugs or relaxation therapy. In view of the heterogeneity of the subjects, we fit a separate linear m...

journal_title：Statistics in medicine

authors： Marler MR,Jacob RG,Lehoczky JP,Shapiro AP

更新日期：1988-06-01 00:00:00

abstract：:Risk prediction models play an important role in prevention and treatment of several diseases. Models that are in clinical use are often refined and improved. In many instances, the most efficient way to improve a successful model is to identify subgroups for which there is a specific biological rationale for improvem...

journal_title：Statistics in medicine

authors： Biswas S,Arun B,Parmigiani G

更新日期：2014-05-20 00:00:00

abstract：:The coefficient of individual equivalence is a permutation-based measure of agreement between two observers making replicated readings on each subject. It compares the observed disagreement between the observers to the expected disagreement under individual equivalence. Individual equivalence of observers requires tha...

journal_title：Statistics in medicine

authors： Pan Y,Haber M,Gao J,Barnhart HX

更新日期：2012-09-10 00:00:00

abstract：:Day and Walter derived methods of joint maximum likelihood estimation for the sojourn time distribution and the false negative rate for a screening programme. Their methods are not directly applicable to a programme which uses alternate screening by two modalities whose sojourn times and false negative rates will diff...

journal_title：Statistics in medicine

authors： Alexander FE

更新日期：1989-06-01 00:00:00

abstract：:Many quantitative assay measurements of metabolites of environmental toxicants in clinical investigations are subject to left censoring due to values falling below assay detection limits. Moreover, when observations occur in both unexposed individuals and exposed individuals who reflect a mixture of two distributions ...

journal_title：Statistics in medicine

authors： Chu H,Kensler TW,Muñoz A

更新日期：2005-07-15 00:00:00

abstract：:This paper investigates the Bayesian procedures for comparing proportions. These procedures are especially suitable for accepting (or rejecting) the equivalence of two population proportions. Furthermore the Bayesian predictive probabilities provide a natural and flexible tool in monitoring trials, especially for choo...

journal_title：Statistics in medicine

authors： Lecoutre B,Derzko G,Grouin JM

更新日期：1995-05-15 00:00:00

abstract：:In designed longitudinal studies, information from the same set of subjects are collected repeatedly over time. The longitudinal measurements are often subject to missing data which impose an analytic challenge. We propose a functional multiple imputation approach modeling longitudinal response profiles as smooth curv...

journal_title：Statistics in medicine

authors： He Y,Yucel R,Raghunathan TE

更新日期：2011-05-10 00:00:00

abstract：:In many studies, a K degree of freedom large sample chi2 test is used to assess the effect of treatment on a multivariate response, such as an omnibus T2-like test of a difference between two treatment groups in any of K repeated measures. Alternately, a K df chi2 test may be used to test the equality of K+1 groups in...

journal_title：Statistics in medicine

authors： Lachin JM,Greenhouse SW,Bautista OM

更新日期：2003-11-15 00:00:00

abstract：:Kappa coefficients are measures of correlation between categorical variables often used as reliability or validity coefficients. We recapitulate development and definitions of the K (categories) by M (ratings) kappas (K x M), discuss what they are well- or ill-designed to do, and summarize where kappas now stand with ...

journal_title：Statistics in medicine

authors： Chmura Kraemer H,Periyakoil VS,Noda A

更新日期：2002-07-30 00:00:00

abstract：:The two tailed Fisher's exact P value is extremely sensitive to small perturbations in 2 x 2 contingency tables. An example indicates that a 1 per cent increase in the denominator of one treatment group results in a 32 per cent drop in the exact P value, but a mere 0.1 per cent decrease in the treatment success rate. ...

journal_title：Statistics in medicine

authors： Dupont WD

更新日期：1986-11-01 00:00:00

abstract：:We simulated multinomial AIDS incidence counts from 27 'representative' AIDS epidemics that spanned a period corresponding to previous applications of backcalculation (1 January 1977 to 1 July 1987) and assessed mean square error for several back-calculated estimators of HIV prevalence and short-term AIDS projections....

journal_title：Statistics in medicine

authors： Rosenberg PS,Gail MH,Pee D

更新日期：1991-08-01 00:00:00

abstract：:In analysis of longitudinal data, the variance matrix of the parameter estimates is usually estimated by the 'sandwich' method, in which the variance for each subject is estimated by its residual products. We propose smooth bootstrap methods by perturbing the estimating functions to obtain 'bootstrapped' realizations ...

journal_title：Statistics in medicine

authors： Li Y,Wang YG

更新日期：2008-03-30 00:00:00

abstract：:To study the spread of sexually transmitted diseases (STDs) using social/sexual mixing models, one must have quantitative information about sexual mixing. An unavoidable complication in gathering such information by survey is that members of the surveyed population will almost certainly have sexual contacts outside th...

journal_title：Statistics in medicine

authors： Rubin G,Umbach D,Shyu SF,Castillo-Chavez C

更新日期：1992-09-15 00:00:00

abstract：:The relative concentration index (RCI) and the absolute concentration index (ACI) have been widely used for monitoring health disparities with ranked health determinants. The RCI has been extended to allow value judgments about inequality aversion by Pereira in 1998 and by Wagstaff in 2002. Previous studies of the ext...

journal_title：Statistics in medicine

authors： Yu M,Liu B,Li Y,Zou ZJ,Breen N

更新日期：2019-01-15 00:00:00

abstract：:Health surveillance involves collecting public health data on chronic and infectious diseases to detect changes in disease incidence rates in order to improve public health. Timely detection of disease clusters is essential in prospective public health surveillance. Most existing health surveillance research is based ...

journal_title：Statistics in medicine

authors： Jiang W,Han SW,Tsui KL,Woodall WH

更新日期：2011-02-28 00:00:00