对美国远程高等教育的认识与思考

美国高校在开展远程教育时有自己的独到之处,它在招生、教学、管理方面真正实现了与现代信息技术的紧密结合,从而营造了发展远程教育的好环境。相比之下,我国远程教育在学生学习动机、教学管理、技术应用、学习支持服务等方面存在着不小的差距,需要在宏观规划、媒体使用、制度建设等方面做进一步的改进。惟此,才能保证远程教育沿着健康的道路顺利向前发展。     

An exploration of the differential usage of residential childcare across national boundaries

The use of residential placements for children needing out‐of‐home care remains controversial. This article considers the discourse of ‘residential’ and ‘institutional’ care before describing, mainly through administrative data sources, the wide variations in group‐care usage in different jurisdictions. In some countries, its use is minimal, with foster care, kinship care and in some cases, adoption being the preferred options. This is not so in other countries where a high percentage of children in care are in residential placements. There is also diversity in the type of residential services, ranging from small group homes to large institutions. The challenges inherent in making process and outcome comparisons across national boundaries are explored. The authors concur with those who argue for more systematic ways of describing and analysing the aims and characteristics of residential settings. Only then can meaningful comparisons be made between outcomes from group‐care regimes in different jurisdictions.     

Likelihood ratio test for one-sided hypothesis of covariance matrices of two normal populations

The likelihood ratio test is derived for a one-sided hypothesis about the covariance matrices from two multivariate normal populations. In the case of equal sample sizes, the limiting distribution of -21og ?_n is given, where ?_n denotes the likelihood ratio criterion. When dimension p=2, for some alternatives, the power of -21og ?_n of size 0.05 is compared with those of several well-known test statistics using Monte Carlo Methods.     

A thurstone-type model for paired comparisons with unequal numbers of repetitions

In paired comparison experiments t objects are ranked for any particular characteristic x by offering the objects in all possible pairs to a judge, each pair being repeated a certain number of times. The judge is to express his preference by giving a score 1 to the preferred object and a score 0 to the non-preferred object. A modification of Thurstone Model for analysis of data from such experiments has been given by Mosteller ‘1951a,b,c’. In this paper angular transformation is used to generalize Mosteller1s model in order to make the preference proportions independent and incidentally ensure homo-scedastlcity of variances and correlations and additivlty of scale in the subjective continuum for the stimuli." The model is extended to unequal numbers of repetitions of the pairs. Using the model two different types of treatment ratings are obtained along with the respective standard errors for moderately large numbers of repetitions, one setting the location parameter S, "0 and the other using the constraint S1 + S2 +…,+ St = 0.     

MULTIPLE COMPARISONS OF LOG-LIKELIHOODS AND COMBINING NONNESTED MODELS WITH APPLICATIONS TO PHYLOGENETIC TREE SELECTION

We consider multiple comparisons of log-likelihood's to take account of the multiplicity of testings in selection of nonnested models. A resampling version of the Gupta procedure for the selection problem is used to obtain a set of good models, which are not significantly worse than the maximum likelihood model; i.e., a confidence set of models. Our method is to test which model is better than the other, while the object of the classical testing methods is to find the correct model. Thus the null hypotheses behind these two approaches are very different. Our method and the other commonly used approaches, such as the approximate Bayesian posterior, the bootstrap selection probability, and the LR test against the full model, are applied to the selection of molecular phylogenetic tree of mammal species. Tree selection is a version of the model-based clustering, which is an example of nonnested model selection. It is shown that the structure of the tree selection problem is equivalent to that of the variable selection problem of the multiple regression with some constraints on the combinations of the variables. It turns out that the LR test rejects all the possible trees because of the misspecification of the models, whereas our method gives a reasonable confidence set. For a better understanding of the uncertainty in the selection, we combine the maximum likelihood estimates (MLE's) of the trees to obtain the full model that includes the trees as the submodels by using a linear approximation of the parametric models. The MLE of the phylogeny is then represented as a network of species rather than a tree. A geometrical interpretation of the problem is also discussed.     

Considerations for Effective Simulation Study Analysis

This article discusses estimation of several percentiles simultaneously, develops a simple test to compare the sizes of two test statistics, and considers the use of logit models to adjust power curves to have the same null hypothesis level.     

Simultaneous tests for finite families of hypotheses

A procedure is proposed whereby R test statistics F=(F₁F₂…F_r)together with "randomly generated critical points" (C₁C₂…C_r) may be used to construct a simultaneous test for

a family containing R hypotheses. This procedure provides simultaneous tests having an exact prescribed type I error rate; the procedure does not require the distribution of F to be known. The simultaneous test is illustrated for making all pairwise comparisons in a one-way ANOVA model.     

The optimal size of choice sets in choice experiments

In this paper, we establish the optimal size of the choice sets in generic choice experiments for asymmetric attributes when estimating main effects only. We give an upper bound for the determinant of the information matrix when estimating main effects and all two-factor interactions for binary attributes. We also derive the information matrix for a choice experiment in which the choice sets are of different sizes and use this to determine the optimal sizes for the choice sets.     

A Nonparametric Test for the Ordered Alternative Based on Kendall's Correlation Coefficient

Several methods have been developed for testing the ordered alternative. These include the Jonckheere–Terpstra (JT) test (Jonckheere, 1954 Jonckheere , A. R. ( 1954 ). A distribution free k-sample test against ordered alternatives . Biometrika 41 : 133 – 145 .[Crossref], [Web of Science ®] , [Google Scholar]; Terpstra, 1952 Terpstra , T. ( 1952 ). The asymptotic normality and consistency of Kendall's test against trend when ties are present in one ranking . Indigationes Mathematicae 14 : 327 – 333 . [Google Scholar]), a modified JT test (MJT) (Tryon and Hettmansperger, 1987 Tryon , V. P. , Hettmansperger , T. P. ( 1987 ). A class of nonparametric tests for homogeneity against ordered alternatives . Annals of Statistics 1 : 1061 – 1070 . [Google Scholar]), and a test proposed by Terpstra and Magel (TM) (Terpstra and Magel, 2003 Terpstra , J. T. , Magel , R. C. ( 2003 ). A new nonparametric test for the ordered alternative problem . Journal of Nonparametric Statistics 15 : 289 – 301 .[Taylor & Francis Online], [Web of Science ®] , [Google Scholar]), among others. This article proposes a new method for testing the ordered alternative. The proposed test is based on Kendall's tau statistic. The asymptotic distribution of the test statistic is given. A Monte Carlo simulation study is conducted comparing the estimated powers of the proposed test with existing tests under a variety of sample sizes and distributions.