11,402 research outputs found
Sparse modeling of categorial explanatory variables
Shrinking methods in regression analysis are usually designed for metric
predictors. In this article, however, shrinkage methods for categorial
predictors are proposed. As an application we consider data from the Munich
rent standard, where, for example, urban districts are treated as a categorial
predictor. If independent variables are categorial, some modifications to usual
shrinking procedures are necessary. Two -penalty based methods for factor
selection and clustering of categories are presented and investigated. The
first approach is designed for nominal scale levels, the second one for ordinal
predictors. Besides applying them to the Munich rent standard, methods are
illustrated and compared in simulation studies.Comment: Published in at http://dx.doi.org/10.1214/10-AOAS355 the Annals of
Applied Statistics (http://www.imstat.org/aoas/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Variable Selection in General Multinomial Logit Models
The use of the multinomial logit model is typically restricted to applications with few predictors, because in
high-dimensional settings maximum likelihood estimates tend to deteriorate. In this paper we are proposing a sparsity-inducing penalty that accounts for the special structure of multinomial models. In contrast to existing methods, it penalizes the parameters that are linked to one variable
in a grouped way and thus yields variable selection instead of parameter selection. We develop a proximal gradient method that is able to efficiently compute stable estimates.
In addition, the penalization is extended to the important case of predictors that vary across response categories. We apply our estimator to the modeling of party choice of voters in Germany including voter-specific variables like age and gender but also party-specific features like stance on nuclear energy and immigration
Medium polarization isotopic effects on nuclear binding energies
There exist several effective interactions whose parameters are fitted to
force mean field predictions to reproduce experimental findings of finite
nuclei and calculated properties of infinite nuclear matter. Exploiting this
tecnique one can give a good description of nuclear binding energies. We
present evidence that further progress can be made by taking into account
medium polarization effects associated with surface and pairing vibrations.Comment: 7 pages, 5 figure
Exclusive electromagnetic production of strangeness on the nucleon : review of recent data in a Regge approach
In view of the numerous experimental results recently released, we provide in
this letter an update on the performance of our simple Regge model for
strangeness electroproduction on the nucleon. Without refitting any parameters,
a decent description of all measured observables and channels is achieved. We
also give predictions for spin transfer observables, recently measured at
Jefferson Lab which have high sensitivity to discriminate between different
theoretical approaches.Comment: 5 pages, 5 figure
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