摘要:

AbstractA binary random variable depends on nonstochastic covariates through a density function. The equations that determine the maximum likelihood estimators of the parameters are intractable and difficult to solve iteratively. We develop modified maximum likelihood estimators for both logistic and nonlo‐gistic densities. These estimators are explicit functions of sample observations and are, therefore, easy to compute. They are asymptotically fully efficient and, for small samples, are almost fully efficient. The appropriateness of the logistic density function is also discusse

ISSN:0323-3847    

DOI:10.1002/bimj.4710390802

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

ISSN:0323-3847    

DOI:10.1002/bimj.4710390803

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractNonparametric statistical analyses of rodent carcinogenicity experiments involving occult tumours of intermediate lethality require numerous interim sacrifices. In recent papers, various semi‐parametric analyses have been proposed which specify a parametric relationship between the death rate in tumour‐bearing and tumour‐free animals as a means of relaxing the requirement for multiple interim sacrifices. These semi‐parametric methods involve different combinations of discrete and continuous time scales for the death and tumour‐onset processes. The effect of combining different scales on this parametric relationship is studied further and illustrated via a

ISSN:0323-3847    

DOI:10.1002/bimj.4710390804

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractIn order to study the agreement between two continuous measurements on a sample of individuals, epidemiologists sometimes partition the original bivariate data into categories defined by the empirical quantiles of the two marginal distributions. The counts in the resulting two‐way contingency table have the empirical bivariate quantile‐partitioned (EBQP) distribution rather than the conventional multinomial distribution. BORKOWF et al. (1997) developed the asymptotic theory and inferential procedures for estimates of measures of agreement calculated from EBQP tables. In this paper, we develop parametric methods for bivariate quantile‐partitioned (BQP) tables. We use these methods to study the efficiency of nonparametric (EBQP) methods and to improve the precision of estimates of measures of agreement. We present computational methods for estimating certain measures of agreement (kappa, weighted kappa, and row proportions) together with their variances. Numerical studies and an example show that nonparametric (EBQP) estimates of kappa and certain row proportions tend to be quite inefficient compared to parametric estimates, whereas nonparametric estimates of weighted kappa can be relatively more efficient for some underlying distributions. Thus, investigators should weigh the efficiency advantages of parametric estimates against possible biases that can result from choosing an inappropriate parametric model when they employ BQP tables to study agre

ISSN:0323-3847    

DOI:10.1002/bimj.4710390805

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractA 2 × 2 table is analyzed from the conditional viewpoint, using Fisher's exact test, for which there is abundant software nowadays (StatXact, SPSS with the module “Exact Test”, …). Nevertheless, because it is well‐nigh impossible to work the test out “by hand”, it is customary in many books to analyze the table, in an approximate fashion, by using the classic chi‐square test with the appropriate continuity correction, and this is what many researchers do in practice. Unfortunately little research has been carried out on the validity conditions of the test (remember the classic advice that the minimum expected quantityEshould be larger than or equal to 5), so that it is applied indiscriminately with the obvious danger of obtaining erroneous results. In this paper the exact validity conditions (which depend not only onE, but also on the real P‐value, on the size of the sample, on the number of tails of the test and on the continuity correction used) are determined, showing that the classic conditionE>5 can be either very strict or quite liberal (depending on the circumstances) and it can even be necessary for the test to haveE>20. A similar study is made of the case of using the binomial approximation, while the Poisson approximation is also discussed.The article ends with a list of rules and precautions to be borne in mind by researchers using the approximate methods. The strict rules are complex enough to make the researcher want to use the exact test, but simplified (and conservative) rules are also given for those

ISSN:0323-3847    

DOI:10.1002/bimj.4710390806

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractOptimal classification rules based on linear functions which maximize the Chernoff distance, or the Morisita distance, or the Kullback‐Leibler distance are studied here. We obtain an expression for the optimal linear discriminant function and show that the resulting linear procedure belongs to the Anderson‐Bahadur admissible class. For the comparison of discriminant rules we use some index which is the measure of the accuracy of a given class of discriminant procedures. The asymptotic form of the discriminant function is also stud

ISSN:0323-3847    

DOI:10.1002/bimj.4710390807

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractA method is described for computing orthogonal projections into finitely generated cones. This method can be used to solve nonnegative least squares approximation problems, to find the multivariate onesided Maximum Likelihood estimator and also determines the most stringent somewhere most powerful test of Schaafsma. The gist of the procedure is the unconstrained maximization of a numerically simple function. This function has a global maximum and allows an uncomplicated maximum search since local maxima do not exist. The maximum can be obtained after a finite number of iterations.

ISSN:0323-3847    

DOI:10.1002/bimj.4710390808

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractThe problem for assessment of equivalence in variability of bioavailability between two drug products is considered. An exact confidence region for the ratio between intrasubject variabilities is derived when the intersubject variance is known. When the intersubject variance is unknown, a large sample approximation is considered. The proposed method for assessing equivalence in variability of bioavailability appears to be asymptotically uncorrelated with the sample mean ratio for average bioavailabilty. As a result, the proposed method in conjunction with the sample mean ratio method can be utilized for assessing population bioequivalence. An example concerning a bioequivalence trial with 24 healthy volunteers is presented to illustrate the proposed method.

ISSN:0323-3847    

DOI:10.1002/bimj.4710390809

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

ISSN:0323-3847    

DOI:10.1002/bimj.4710390801

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY