摘要:

AbstractThe use of extreme discordant sib pairs (EDSP) or extreme concordant sib pairs (ECSP) has recently been proposed to increase power for mapping quantitative traits in humans (RISCH and ZHANG, 1995, 1996). In this paper we propose a test statistic to jointly analyze EDSP and ECSP based on a clinical sampling procedure. This test statistic does not fulfill any optimality criteria. However, this approach is useful for quantitative traits of clinical significance for which EDSP are rare and/or expensive to ascertain. We show how sample size calculations can be adjusted for recombination using single markers, multipoint analysis, incompletely polymorphic markers and varying proportions of ECSP. If the true genetic model is unknown, the combined approach appears to be more robust than sampling based on only EDSP or only ECSP. We discuss how to find the optimal proportion of EDSP and ECSP to be included in an analysis under power considerations.

ISSN:0323-3847    

DOI:10.1002/bimj.4710390302

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractIn order to control linkage experiments, exact formulas and approximations are derived for the minimum distance between quantitative trait loci and the nearest marker locus. The locations of the loci are assumed to be uniformly distributed over the genome. The locations of the marker loci may be known or unknown. The number and length of the chromosomes are arbitrary and therefore the results are applicable for all kinds of species. Analogous formulas are derived for the maximum distance between the quantitative trait loci and the nearest marker loci. For the probability of linkage more simple expressions are derived. The accuracy of the approximations is checked by a simulation.

ISSN:0323-3847    

DOI:10.1002/bimj.4710390303

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractFor a diallel model (TOPHAM, 1966) estimators of variance components are obtained by adopting the general approach outlined by SEELY (1969, 1970, 1971), SEELY and ZYSKIND (1971) and YUAN (1977) in the case of unbalanced data.

ISSN:0323-3847    

DOI:10.1002/bimj.4710390304

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractA method for reducing bias in observational studies proposed by ROSENBAUM and RUBIN (1983, 1984) is discussed with a view to applications in studies designed to compare two treatments. The data are stratified on a function of covariates, called the propensity score. The propensity score is the conditional probability of receiving a specific treatment given a set of observed covariates. Some insight into how this kind of stratification works in theory is given. Within strata, the treatment groups are comparable with respect to the distribution of covariates incorporated into the score, hence a corresponding stratified analysis can be considered. The method is different from other strategies in that the sub‐classes are not intended to comprise patients with similar prognosis. In practice, estimated grouped scores are used. Problems concerning the interpretation of the proposed stratified approach are illustrated by an application in oncology, and the results are compared to those from an analysis in a standard regression mode

ISSN:0323-3847    

DOI:10.1002/bimj.4710390305

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractA method for analyzing correlated binary outcomes when the responses are distinct measurements made simultaneously on a single individual is presented. This extension of univariate logistic regression allows us to model the dependence of the responses on a set of covariates while estimating the degree of association among them. For the case of two dichotomous outcomes, a form of the cumulative bivariate logistic distribution proposed by Gumbel is used to characterize their joint probabilities in terms of logistic marginal probabilities and the correlation coefficient of the responses. The model is then extended to accommodate three or more dichotomous outcomes. A two‐step approximation to fitting the multivariate logistic model is also describe

ISSN:0323-3847    

DOI:10.1002/bimj.4710390306

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractIn the statistical evaluation of data from a dose‐response experiment, it is frequently of interest to test for dose‐related trend: an increasing trend in response with increasing dose. The randomization trend test, a generalization of Fisher's exact test, has been recommended for animal tumorigenicity testing when the numbers of tumor occurrences are small. This paper examines the type I error of the randomization trend test, and the Cochran‐Armitage and Mantel‐Haenszel tests. Simulation results show that when the tumor incidence rates are less than 10%, the randomization test is conservative; the test becomes very conservative when the incidence rate is less than 5%. The Cochran‐Armitage and Mantel‐Haenszel tests are slightly anti‐conservative (liberal) when the incidence rates are larger than 3%. Further, we propose a less conservatived method of calculating the p‐value of the randomization trend test by excluding some permutations whose probabilities of occurrence are greater than the probability of the the o

ISSN:0323-3847    

DOI:10.1002/bimj.4710390307

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractThis paper considers the use of ante‐dependence models in problems with repeated measures through time. These are conditional regression models which reflect the dependence of a measure on some of the previous observations from the same subject. We present maximum likelihood estimators of the covariance matrix and procedures for selecting the order of ante‐degendence based on penalized like‐lihoods. Extensions to missing data situations are discussed.We propose Wald‐type test statistics and apply them in two situations common in experiments with repeated measures: one with pre‐study observations and another one with small sample size relative to the number of time periods. In these examples, tests assuming ante‐dependence find effects which are not detected using competing

ISSN:0323-3847    

DOI:10.1002/bimj.4710390308

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractLoglinear symmetry and quasi‐symmetry models are proposed as tools for investigating various hypotheses about change. First, a survey of model representations is provided, including model specification in terms of hierarchical loglinear models and in design matrix notation. Secondly, the range of symmetry and quasi‐symmetry models is extended to the joint analysis of several groups. Parameter constraints are discussed which allow one to test specific hypotheses about group differences in symmetric frequency distributions. Finally, symmetry and quasi‐symmetry models are considered for multiway contigency tables. In this context, loglinear total score models are proposed for the analysis of symmetry in several marginal distributions. The proposed models reflect cross‐sectional as well as longitudinal facets of deve

ISSN:0323-3847    

DOI:10.1002/bimj.4710390309

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractThis paper introduces a novel model selection procedure for tree‐based classifiers. The method is based on the bootstrap 632+ rule recently proposed by Efron and Tibshirani. The rule allows selecting compact, non‐overfitting classification trees by weighting the contributions of the resubstitution and standard bootstrap estimated error. The proposed method is applied in a medical entomology problem for modeling the risk of parasite prese

ISSN:0323-3847    

DOI:10.1002/bimj.4710390310

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

ISSN:0323-3847    

DOI:10.1002/bimj.4710390311

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY