Abstract:
:In longitudinal studies with incomplete data, where the number of time points can become numerous, it is often advantageous to model the covariance matrix. We describe several covariance models (for example, mixed models, compound symmetry, AR(1)-type models, and combination models) that offer parsimonious alternatives to unstructured sigma. We evaluate each covariance model with longitudinal data concerning cholesterol as the repeated outcome measure. We discuss strategies for deciding the 'best' model and show a graphical technique for judging goodness-of-fit of covariance models.
journal_name
Stat Medjournal_title
Statistics in medicineauthors
Grady JJ,Helms RWdoi
10.1002/sim.4780141302subject
Has Abstractpub_date
1995-07-15 00:00:00pages
1397-416issue
13eissn
0277-6715issn
1097-0258journal_volume
14pub_type
杂志文章,评审abstract::It is naive and incorrect to use the proportions of successful operations to compare the performance of surgeons because the patients' risk profiles are different. In this paper, we explore the use of risk-adjusted procedures to compare the performance of surgeons. One such risk-adjusted statistic is the standardized ...
journal_title:Statistics in medicine
pub_type: 杂志文章
doi:10.1002/sim.7310
更新日期:2017-07-20 00:00:00
abstract::We study the group bridge and the adaptive group bridge penalties for competing risks quantile regression with group variables. While the group bridge consistently identifies nonzero group variables, the adaptive group bridge consistently selects variables not only at group level but also at within-group level. We all...
journal_title:Statistics in medicine
pub_type: 杂志文章
doi:10.1002/sim.7619
更新日期:2018-04-30 00:00:00
abstract::The objective of a phase II cancer clinical trial is to screen a treatment that can produce a similar or better response rate compared to the current treatment results. This screening is usually carried out in two stages as proposed by Simon. For ineffective treatment, the trial should terminate at the first stage. En...
journal_title:Statistics in medicine
pub_type: 杂志文章
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更新日期:1997-12-15 00:00:00
abstract::When estimating the average effect of a binary treatment (or exposure) on an outcome, methods that incorporate propensity scores, the G-formula, or targeted maximum likelihood estimation (TMLE) are preferred over naïve regression approaches, which are biased under misspecification of a parametric outcome model. In con...
journal_title:Statistics in medicine
pub_type: 杂志文章
doi:10.1002/sim.7628
更新日期:2018-07-20 00:00:00
abstract::Arming the immune system against cancer has emerged as a powerful tool in oncology during recent years. Instead of poisoning a tumor or destroying it with radiation, therapeutic cancer vaccine, a type of cancer immunotherapy, unleashes the immune system to combat cancer. This indirect mechanism-of-action of vaccines p...
journal_title:Statistics in medicine
pub_type: 杂志文章
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更新日期:2017-02-20 00:00:00
abstract::Systematic reviews often provide recommendations for further research. When meta-analyses are inconclusive, such recommendations typically argue for further studies to be conducted. However, the nature and amount of future research should depend on the nature and amount of the existing research. We propose a method ba...
journal_title:Statistics in medicine
pub_type: 杂志文章
doi:10.1002/sim.5524
更新日期:2013-01-15 00:00:00
abstract::We describe the usual statistical concepts and consequent appropriate simulations of a prospective study for the simple case of a single risk variable and an assumed logistic model. We examine the simulations of Lilienfeld and Pyne, and show that they are seriously flawed. Contrary to those authors' claims, the estima...
journal_title:Statistics in medicine
pub_type: 杂志文章
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更新日期:1985-04-01 00:00:00
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journal_title:Statistics in medicine
pub_type: 杂志文章
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更新日期:2015-06-15 00:00:00
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journal_title:Statistics in medicine
pub_type: 杂志文章
doi:10.1002/sim.5624
更新日期:2013-04-15 00:00:00
abstract::A mixture model incorporating long-term survivors has been adopted in the field of biostatistics where some individuals may never experience the failure event under study. The surviving fractions may be considered as cured. In most applications, the survival times are assumed to be independent. However, when the survi...
journal_title:Statistics in medicine
pub_type: 杂志文章
doi:10.1002/sim.932
更新日期:2001-06-15 00:00:00
abstract::Many reactions in enzymology are governed by the Michaelis-Menten equation. Characterising these reactions requires the estimation of the parameters K(M) and V(max) which determine the Michaelis-Menten equation and this is done by observing rates of reactions at a set of substrate concentrations. The choice of substra...
journal_title:Statistics in medicine
pub_type: 杂志文章
doi:10.1002/sim.1612
更新日期:2004-02-15 00:00:00
abstract::This article deals with determination of a sample size that guarantees the success of a trial. We follow a Bayesian approach and we say an experiment is successful if it yields a large posterior probability that an unknown parameter of interest (an unknown treatment effect or an effects-difference) is greater than a c...
journal_title:Statistics in medicine
pub_type: 杂志文章
doi:10.1002/sim.3175
更新日期:2008-06-15 00:00:00
abstract::In a typical bioequivalence trial, summary measures of the plasma concentration versus time profile are used to compare two formulations of a drug product. Commonly used measures include area under the curve (AUC), maximum plasma concentration (C(max)) and time to maximum concentration (T(max)). Equivalence of these s...
journal_title:Statistics in medicine
pub_type: 杂志文章
doi:10.1002/1097-0258(20001030)19:20<2855::aid-sim550>
更新日期:2000-10-30 00:00:00
abstract::The construction, validation and updating of a prognostic model for kidney graft survival is reported using data from the Eurotransplant database. First, a model is constructed for data from transplantations in the period 1984 to 1987. The model is later updated for the 1988 1990 data. The first data set was randomly ...
journal_title:Statistics in medicine
pub_type: 杂志文章
doi:10.1002/sim.4780141806
更新日期:1995-09-30 00:00:00
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journal_title:Statistics in medicine
pub_type: 杂志文章
doi:10.1002/sim.2469
更新日期:2006-11-15 00:00:00
abstract::Pearson's chi-squared, the likelihood-ratio, and Fisher-Freeman-Halton's test statistics are often used to test the association of unordered r x c tables. Asymptotical, exact conditional, or exact conditional with mid-p adjustment methods are commonly used to compute the p-value. We have compared test power and signif...
journal_title:Statistics in medicine
pub_type: 杂志文章
doi:10.1002/sim.2839
更新日期:2007-10-15 00:00:00
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journal_title:Statistics in medicine
pub_type: 杂志文章
doi:10.1002/sim.2070
更新日期:2005-06-30 00:00:00
abstract::Exploring the possible reasons for heterogeneity between studies is an important aspect of conducting a meta-analysis. This paper compares a number of methods which can be used to investigate whether a particular covariate, with a value defined for each study in the meta-analysis, explains any heterogeneity. The main ...
journal_title:Statistics in medicine
pub_type: 杂志文章
doi:10.1002/(sici)1097-0258(19991030)18:20<2693::aid-s
更新日期:1999-10-30 00:00:00
abstract::Measures that quantify the impact of heterogeneity in univariate meta-analysis, including the very popular I(2) statistic, are now well established. Multivariate meta-analysis, where studies provide multiple outcomes that are pooled in a single analysis, is also becoming more commonly used. The question of how to quan...
journal_title:Statistics in medicine
pub_type: 杂志文章
doi:10.1002/sim.5453
更新日期:2012-12-20 00:00:00
abstract:BACKGROUND:It has been recommended that onset of antidepressant action be assessed using survival analyses with assessments taken at least twice per week. However, such an assessment schedule is problematic to implement. The present study assessed the feasibility of comparing onset of action between treatments using a ...
journal_title:Statistics in medicine
pub_type: 杂志文章
doi:10.1002/sim.2309
更新日期:2006-07-30 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::Mesothelioma is a rare cancer caused by exposure to asbestos. Belgium has a known long history of asbestos production, resulting in one of the highest mesothelioma mortality rates worldwide. While the production of asbestos has stopped completely, the long latency period of mesothelioma, which can fluctuate between 20...
journal_title:Statistics in medicine
pub_type: 杂志文章
doi:10.1002/sim.8697
更新日期:2020-11-20 00:00:00
abstract::Many randomized clinical trials include a data and safety monitoring board (DSMB) that is responsible for reviewing accruing data, monitoring performance of the trial, assuring safety of the participants in the trial, and assessing the efficacy of treatment. The DSMB often makes recommendations about continuation of t...
journal_title:Statistics in medicine
pub_type: 杂志文章
doi:10.1002/sim.4780120504
更新日期:1993-03-01 00:00:00
abstract::Providing personalized treatments designed to maximize benefits and minimizing harms is of tremendous current medical interest. One problem in this area is the evaluation of the interaction between the treatment and other predictor variables. Treatment effects in subgroups having the same direction but different magni...
journal_title:Statistics in medicine
pub_type: 杂志文章
doi:10.1002/sim.5429
更新日期:2012-12-10 00:00:00
abstract::For each of 211 arteriosclerosis obliterans patients, the degree of stenosis of arteries at four sites were examined at Hiroshima University Hospital to analyse the relationship between the degree of stenosis and age, sex and site. The generalized estimating equations using a proportional odds model for the stenosis p...
journal_title:Statistics in medicine
pub_type: 杂志文章
doi:10.1002/sim.1363
更新日期:2003-07-15 00:00:00
abstract::The primary goal of a phase I trial is to find the maximally tolerated dose (MTD) of a treatment. The MTD is usually defined in terms of a tolerable probability, q(*), of toxicity. Our objective is to find the highest dose with toxicity risk that does not exceed q(*), a criterion that is often desired in designing pha...
journal_title:Statistics in medicine
pub_type: 杂志文章
doi:10.1002/sim.970
更新日期:2002-01-15 00:00:00
abstract::In this paper, we consider fitting a flexible and interpretable additive regression model in a data-rich setting. We wish to avoid pre-specifying the functional form of the conditional association between each covariate and the response, while still retaining interpretability of the fitted functions. A number of recen...
journal_title:Statistics in medicine
pub_type: 杂志文章
doi:10.1002/sim.7859
更新日期:2019-02-20 00:00:00
abstract::The treatment effect sizes that can be detected with sufficient power up to the different interim analyses constitute a clinically meaningful criterion for the selection of a group sequential test for a clinical trial. For any pre-specified sequence of effect sizes, it is possible to construct group sequential boundar...
journal_title:Statistics in medicine
pub_type: 杂志文章
doi:10.1002/sim.1751
更新日期:2004-05-15 00:00:00
abstract::We consider recurrent events of the same type that occur during alternating restraint and non-restraint time periods. This research is motivated by a study on juvenile recidivism, where the probationers were followed for re-offenses during alternating placement periods and free-time periods. During the placement perio...
journal_title:Statistics in medicine
pub_type: 杂志文章
doi:10.1002/sim.7150
更新日期:2017-02-20 00:00:00
abstract::This paper presents tables analogous to T-tables for use in the 2 x 2 multinomial trial, where the continuity corrected Z-statistic is used to make exact unconditional inference. This is the first solution of a discrete exact unconditional inference problem involving a multivariate nuisance parameter for which no anci...
journal_title:Statistics in medicine
pub_type: 杂志文章
doi:10.1002/sim.4780110708
更新日期:1992-05-01 00:00:00