115,020 research outputs found
Generating Correlated Ordinal Random Values
Ordinal variables appear in many field of statistical research. Since working with simulated data is an accepted technique to improve models or test results there is a need for providing correlated ordinal random values with certain properties like marginal distribution and correlation structure. The present paper describes two methods for generating such values: binary conversion and a mean mapping approach. The algorithms of the two methods are described and some examples of the outcomes are shown
Exchangeable Variable Models
A sequence of random variables is exchangeable if its joint distribution is
invariant under variable permutations. We introduce exchangeable variable
models (EVMs) as a novel class of probabilistic models whose basic building
blocks are partially exchangeable sequences, a generalization of exchangeable
sequences. We prove that a family of tractable EVMs is optimal under zero-one
loss for a large class of functions, including parity and threshold functions,
and strictly subsumes existing tractable independence-based model families.
Extensive experiments show that EVMs outperform state of the art classifiers
such as SVMs and probabilistic models which are solely based on independence
assumptions.Comment: ICML 201
Jet Substructure Without Trees
We present an alternative approach to identifying and characterizing jet
substructure. An angular correlation function is introduced that can be used to
extract angular and mass scales within a jet without reference to a clustering
algorithm. This procedure gives rise to a number of useful jet observables. As
an application, we construct a top quark tagging algorithm that is competitive
with existing methods.Comment: 22 pages, 16 figures, version accepted by JHE
Four-point correlation function of stress-energy tensors in N=4 superconformal theories
We derive the explicit expression for the four-point correlation function of
stress-energy tensors in four-dimensional N=4 superconformal theory. We show
that it has a remarkably simple and suggestive form allowing us to predict a
large class of four-point correlation functions involving the stress-energy
tensor and other conserved currents. We then apply the obtained results on the
correlation functions to computing the energy-energy correlations, which
measure the flow of energy in the final states created from the vacuum by a
source. We demonstrate that they are given by a universal function independent
of the choice of the source. Our analysis relies only on N=4 superconformal
symmetry and does not use the dynamics of the theory.Comment: 31 pages; v2: references adde
Sample Selectivity and the Validity of International Student Achievement Tests in Economic Research
Critics of international student comparisons argue that results may be influenced by differences in the extent to which countries adequately sample their entire student populations. In this research note, we show that larger exclusion and non-response rates are related to better country average scores on international tests, as are larger enrollment rates for the relevant age group. However, accounting for sample selectivity does not alter existing research findings that tested academic achievement can account for a majority of international differences in economic growth and that institutional features of school systems have important effects on international differences in student achievement.economic growth, international student achievement tests, sample selection, educational production
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