6,841 research outputs found

    An enquiry into the predictive value of grammar school entrance examinations

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    To sail the new ocean of space

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    Space effort by united state

    Statistical analysis on high-dimensional spheres and shape spaces

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    We consider the statistical analysis of data on high-dimensional spheres and shape spaces. The work is of particular relevance to applications where high-dimensional data are available--a commonly encountered situation in many disciplines. First the uniform measure on the infinite-dimensional sphere is reviewed, together with connections with Wiener measure. We then discuss densities of Gaussian measures with respect to Wiener measure. Some nonuniform distributions on infinite-dimensional spheres and shape spaces are introduced, and special cases which have important practical consequences are considered. We focus on the high-dimensional real and complex Bingham, uniform, von Mises-Fisher, Fisher-Bingham and the real and complex Watson distributions. Asymptotic distributions in the cases where dimension and sample size are large are discussed. Approximations for practical maximum likelihood based inference are considered, and in particular we discuss an application to brain shape modeling.Comment: Published at http://dx.doi.org/10.1214/009053605000000264 in the Annals of Statistics (http://www.imstat.org/aos/) by the Institute of Mathematical Statistics (http://www.imstat.org

    The Exploration of Space

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    Bayesian matching of unlabelled point sets using Procrustes and configuration models

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    The problem of matching unlabelled point sets using Bayesian inference is considered. Two recently proposed models for the likelihood are compared, based on the Procrustes size-and-shape and the full configuration. Bayesian inference is carried out for matching point sets using Markov chain Monte Carlo simulation. An improvement to the existing Procrustes algorithm is proposed which improves convergence rates, using occasional large jumps in the burn-in period. The Procrustes and configuration methods are compared in a simulation study and using real data, where it is of interest to estimate the strengths of matches between protein binding sites. The performance of both methods is generally quite similar, and a connection between the two models is made using a Laplace approximation

    The Structure of Early Care and Education in the United States: Historical Evolution and International Comparisons

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    Most European governments have universal, consolidated, education-based ECE programs that are available from early in the morning to late in the evening throughout the year. European ECE programs are uniformly of high quality, generally last at least three years, and are funded to serve all children. The US ECE system is composed of three separate programs (Head Start, Pre-Kindergarten (Pre-K) and the child care voucher program) targeted to low-income children. With a few notable exceptions, US ECE programs are funded to serve less than half of the eligible children. US ECE programs developed quite separately. They have different goals, different funding sources, different administrations and policies, and generally last for an academic year or less. Pre-K and Head Start operate only 3 to 6 hours a day and are open only during the academic year. The average quality of US ECE programs is generally much lower than the average quality of European ECE programs. Further, the quality of US ECE programs varies widely even within local areas. Although the US has greatly increased expenditures on ECE, US governments pay only 40% of the costs of ECE, while European governments pay 70% to 90% of the costs of ECE. None of the major US ECE programs simultaneously provides work supports for parents, child development opportunities for children and preparation for school for low-income children. The evidence suggests that the US ECE system is neither efficient nor equitable. Consolidation of funding and administration of current US ECE programs could substantially lower transaction costs for parents and provide more stable care arrangements for children. Increased funding could improve the quality of existing programs, extend hours and months of operation, and make care available to all eligible families. Both the evaluation literature and the European experience suggest that such a consolidated, well-funded system could be successful in preparing poor children for school. Further, the benefits of such a program could well exceed the costs since it is precisely low-income children that benefit most from stable, high-quality ECE. However, such a targeted program will have neither the positive peer group effects nor the social-integration benefits of universal ECE programs.
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