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Longhai Li - One of the best experts on this subject based on the ideXlab platform.
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A New Regression Model: Modal Linear Regression.
Scandinavian Journal of Statistics, 2013Co-Authors: Longhai LiAbstract:type="main" xml:id="sjos12054-abs-0001"> The mode of a distribution provides an important summary of data and is often estimated on the basis of some non-parametric kernel density estimator. This article develops a new data analysis tool called modal linear regression in order to explore high-dimensional data. Modal linear regression models the conditional mode of a response Y given a set of predictors x as a linear function of x . Modal linear regression differs from standard linear regression in that standard linear regression models the conditional mean (as opposed to mode) of Y as a linear function of x . We propose an expectation–maximization algorithm in order to estimate the regression coefficients of modal linear regression. We also provide asymptotic properties for the proposed estimator without the symmetric assumption of the error density. Our empirical studies with simulated data and real data demonstrate that the proposed modal regression gives shorter predictive intervals than mean linear regression, median linear regression and MM-estimators.
Claudia Pahl-wostl - One of the best experts on this subject based on the ideXlab platform.
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Evaluating group model building exercises: a method for comparing externalized mental models and group models
System Dynamics Review, 2015Co-Authors: Geeske Scholz, Martina Austermann, Kai Kaldrack, Claudia Pahl-wostlAbstract:We introduce a systematic method to compare externalized mental models with a group model resulting from a group model building (GMB) process. To this end, we categorize the various concepts included in the models, and propose Venn diagrams and matrices to demonstrate the composition of the group model and identify the overlapping categories. We then suggest a set of metrics to analyze the matrices. We apply our method to a dataset of three GMB processes, finding the suggested method to be helpful for evaluating the extent to which all participants were able to include their perspectives, and whether new ideas emerged from the process, thus constituting innovation. We conclude that our method may be a valuable contribution to the evaluation of GMB processes. Furthermore, we demonstrate that the categorization of the concepts is a delicate process and has a significant influence on the results. Copyright © 2015 System Dynamics Society
Toshio Yamagata - One of the best experts on this subject based on the ideXlab platform.
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Subtropical Dipole Modes Simulated in a Coupled General Circulation Model
Journal of Climate, 2012Co-Authors: Yushi Morioka, Tomoki Tozuka, Sébastien Masson, Pascal Terray, Jing-jia Luo, Toshio YamagataAbstract:The growth and decay mechanisms of subtropical dipole modes in the southern Indian and South Atlantic Oceans and their impacts on southern African rainfall are investigated using results from a coupled general circulation model originally developed for predicting tropical climate variations. The second (most) dominant mode of interannual sea surface temperature (SST) variations in the southern Indian (South Atlantic) Ocean represents a northeast–southwest oriented dipole, now called subtropical dipole mode. The positive (negative) SST interannual anomaly pole starts to grow in austral spring and reaches its peak in February. In austral late spring, the suppressed (enhanced) latent heat flux loss associated with the variations in the subtropical high causes a thinner (thicker) than normal mixed layer thickness that, in turn, enhances (reduces) the warming of the mixed layer by the climatological shortwave radiation. The positive (negative) pole gradually decays in austral fall because the mixed layer cooling by the entrainment is enhanced (reduced), mostly owing to the larger (smaller) temperature difference between the mixed layer and the entrained water. The increased (decreased) latent heat loss due to the warmer (colder) SST also contributes to the decay of the positive (negative) pole. Although further verification using longer observational data is required, the present coupled model suggests that the South Atlantic subtropical dipole may play a more important role in rainfall variations over the southern African region than the Indian Ocean subtropical dipole.
Kerk L Phillips - One of the best experts on this subject based on the ideXlab platform.
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integrating microsimulation models of tax policy into a dge macroeconomic model
Public Finance Review, 2019Co-Authors: Jason Matthew Debacker, Richard Evans, Kerk L PhillipsAbstract:This article proposes a method for integrating individual effective tax rates and marginal tax rates computed from a microsimulation (partial equilibrium) model of tax policy with a dynamic general equilibrium model of tax policy that can provide macroeconomic analysis or dynamic scores of tax reforms. Our approach captures the rich heterogeneity, realistic demographics, and tax-code detail of the microsimulation model and allows this detail to inform a general equilibrium model with a relatively high degree of heterogeneity. In addition, we propose a functional form in which tax rates depend jointly on the levels of both capital income and labor income.
Thomas Cartier-michaud - One of the best experts on this subject based on the ideXlab platform.
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A gyro-kinetic model for trapped electron and ion modes
The European Physical Journal D, 2014Co-Authors: Thomas Drouot, Etienne Gravier, T. Réveillé, Pierre Bertrand, Alain Ghizzo, Y Sarazin, Xavier Garbet, Thomas Cartier-michaudAbstract:In tokamak plasmas, it is recognized that ITG (ion temperature gradient instability) and trapped electron modes (TEM) are held responsible for turbulence giving rise to anomalous transport. The present work focuses on the building of a model including trapped kinetic ions and trapped kinetic electrons. For this purpose, the dimensionality is reduced by averaging the motion over the cyclotron motion and the “banana” orbits, according to the fact that the instabilities are characterized by frequencies of the order of the low trapped particle precession frequency. Moreover, a set of action-angle variables is used. The final model is 4D (two-dimensional phase space parametrized by the two first adiabatic invariants namely the particle energy and the trapping parameter). In this paper, the trapped ion and electron modes (TIM and TEM) are studied by using a linear analysis of the model. This work is currently performed in order to include trapped electrons in an existing semi lagrangian code for which TIM modes are already taken into account. This study can be considered as a first step in order to include kinetic trapped electrons in the 5D gyrokinetic code GYSELA [J. Abiteboul et al., ESAIM Proc. 32, 103 (2011)].
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A gyro-kinetic model for trapped electron and ion modes
The European Physical Journal D : Atomic molecular optical and plasma physics, 2014Co-Authors: Thomas Drouot, Etienne Gravier, T. Réveillé, Pierre Bertrand, Alain Ghizzo, Y Sarazin, Xavier Garbet, Thomas Cartier-michaudAbstract:In tokamak plasmas, it is recognized that ITG (ion temperature gradient instability) and trapped electron modes (TEM) are held responsible for turbulence giving rise to anomalous transport. The present work focuses on the building of a model including trapped kinetic ions and trapped kinetic electrons. For this purpose, the dimensionality is reduced by averaging the motion over the cyclotron motion and the ``banana'' orbits, according to the fact that the instabilities are characterized by frequencies of the order of the low trapped particle precession frequency. Moreover, a set of action-angle variables is used. The final model is 4D (two-dimensional phase space parametrized by the two first adiabatic invariants namely the particle energy and the trapping parameter). In this paper, the trapped ion and electron modes (TIM and TEM) are studied by using a linear analysis of the model. This work is currently performed in order to include trapped electrons in an existing semi lagrangian code for which TIM modes are already taken into account. This study can be considered as a first step in order to include kinetic trapped electrons in the 5D gyrokinetic code GYSELA.