摘要:

AbstractTwo common goals when choosing a method for performing all pairwise comparisons ofJindependent groups are controlling experiment wise Type I error and maximizing power. Typically groups are compared in terms of their means, but it has been known for over 30 years that the power of these methods becomes highly unsatisfactory under slight departures from normality toward heavy‐tailed distributions. An approach to this problem, well‐known in the statistical literature, is to replace the sample mean with a measure of location having a standard error that is relatively unaffected by heavy tails and outliers. One possibility is to use the trimmed mean. This paper describes three such multiple comparison procedures and compares them to two methods for comparing me

ISSN:0323-3847    

DOI:10.1002/bimj.4710370602

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractA one‐year birth cohort from Northern Finland has been followed up since 1966. As a part of this study, we are in this paper concerned with analysing the progression of myopia (nearsightness) up to the age of 20 years. The random coefficient regression model was chosen for the analysis because of the large individual variation in the development of myopia. Maximum likelihood estimates for the parameters in the model were obtained via the expectation maximization (EM) algorithm. It is shown how the estimated model can be used to predict future observations for an individual using the previously recorded refractive error measurements as well as other relevant data on the patient in questio

ISSN:0323-3847    

DOI:10.1002/bimj.4710370603

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractThe problem of assessing the relative calibrations and relative accuracies of a set ofpinstruments, each designed to measure the same characteristic on a common group of individuals is considered by using the EM algorithm. As shown, the EM algorithm provides a general solution for this problem. Its implementation is simple and in its most general form requires no extra iterative procedures within the M step. One important feature of the algorithm in this set up is that the error variance estimates are always positive. Thus, it can be seen as a kind of restricted maximization procedure. The expected information matrix for the maximum likelihood estimators is derived, upon which the large sample estimated covariance matrix for the maximum likelihood estimators can be computed. The problem of testing hypothesis about the calibration lines can be approached by using the Wald statistics. The approach is illustrated by re‐analysing two data sets in the literatur

ISSN:0323-3847    

DOI:10.1002/bimj.4710370604

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractA nonparametric discrete delta method for estimating standard errors of percentile estimators in quantal bioassay is described. A simulation study of confidence intervals for EDxin probit analysis shows the discrete delta method compared favorably with intervals based on maximum likelihood and also some parametric bootstrap methods.

ISSN:0323-3847    

DOI:10.1002/bimj.4710370605

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractThis paper proposes the use of hidden Markov time series models for the analysis of the behaviour sequences of one or more animals under observation. These models have advantages over the Markov chain models commonly used for behaviour sequences, as they can allow for time‐trend or expansion to several subjects without sacrificing parsimony. Furthermore, they provide an alternative to higher‐order Markov chain models if a first‐order Markov chain is unsatisfactory as a model. To illustrate the use of such models, we fit multivariate and univariate hidden Markov models allowing for time‐trend to data from an experiment investigating the effects of feeding on the locomotory behaviour of locusts (Locusta migr

ISSN:0323-3847    

DOI:10.1002/bimj.4710370606

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractNeural networks have received much attention in recent years mostly by non‐statisticians. The purpose of this paper is to incorporate neural networks in a non‐linear regression model and obtain maximum likelihood estimates of the network parameters using a standard Newton‐Raphson algorithm. We use maximum likelihood estimators instead of the usual back‐propagation technique and compare the neural network predictions with predictions of quadratic regression models and with non‐parametric nearest neighbor predictions. These comparisons are made using data generated from a variety of functions. Because of the number of parameters involved, neural network models can easily over‐fit the data, hence validation of results

ISSN:0323-3847    

DOI:10.1002/bimj.4710370607

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

ISSN:0323-3847    

DOI:10.1002/bimj.4710370608

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractUsing the variance stabilizing technique, a product multinomial model is introduced to generate a new statistic to test observers' uncertainty in a weighted concordance analysis. Distance matrices which follow some specific rules are obtained by linear combinations of hierarchical distance matrices whose elements are equal to 0 or 1 and unit diagonal. The new statistic is compared with the kappa statistic interpreted by considering the covariance matrix generated by the data. By rewriting the test statistic in a barycentric form, one demonstrates how to modify the barycentric coefficients to derive an adequate measure of the interobserver agreement. The methods are illustrated using two examples.

ISSN:0323-3847    

DOI:10.1002/bimj.4710370609

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

ISSN:0323-3847    

DOI:10.1002/bimj.4710370610

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractApproximate nonparametric maximum likelihood estimation of the tumor incidence rate and comparison of tumor incidence rates between treatment groups are examined in the context of animal carcinogenicity experiments that have interval sacrifice data but lack cause‐of‐death information. The estimation procedure introduced by MALANI and VAN RYZIN (1988), which can result in a negative estimate of the tumor incidence rate, is modified by employing a numerical method to maximize the likelihood function iteratively, under the constraint that the tumor incidence rate is nonnegative. With the new procedure, estimates can be obtained even if sacrifices occur anywhere within an interval. The resulting estimates have reduced standard error and give more power to the test of two heterogeneous groups. Furthermore, a linear contrast of more than two groups can be tested using our procedure. The proposed estimation and testing methods are illustrated with an experimental data

ISSN:0323-3847    

DOI:10.1002/bimj.4710370611

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY