Olcay Arslan

Weighted LAD-LASSO method for robust parameter estimation and variable selection in regression

The weighted least absolute deviation (WLAD) regression estimation method and the adaptive least absolute shrinkage and selection operator (LASSO) are combined to achieve robust parameter estimation and variable selection in regression simultaneously. Compared with the LAD-LASSO method, the weighted LAD-LASSO (WLAD-LASSO) method will resist to the heavy-tailed errors and outliers in explanatory variables. Properties of the WLAD-LASSO estimators are investigated. A small simulation study and an example are provided to demonstrate the superiority of the WLAD-LASSO method over the LAD-LASSO method in the presence of outliers in the explanatory variables and the heavy-tailed error distribution.

One-step M -estimators: Jones and Faddy's skewed t -distribution

One-step M (OSM)-estimator needs some initial/preliminary estimates at the beginning of the calculation process. In this study, we propose to use new initial estimates for the calculation of the OSM-estimator. We consider simple location and simple linear regression models when the distribution of the error terms is Jones and Faddys skewed t. Monte-Carlo simulation study shows that the OSM estimator(s) based on the proposed initial estimates is/are more efficient than the OSM estimator(s) based on the traditional initial estimates especially for the skewed cases. We also analyze some real data sets taken from the literature at the end of the paper.

Robust Mixture Regression Based on the Skew t Distribution

In this study, we propose a robust mixture regression procedure based on the skew t distribution to model heavy-tailed and/or skewed errors in a mixture regression setting. Using the scale mixture representation of the skew t distribution, we give an Expectation Maximization (EM) algorithm to compute the maximum likelihood (ML) estimates for the paramaters of interest. The performance of proposed estimators is demonstrated by a simulation study and a real data example.

Robust Mixture Regression Using Mixture of Different Distributions

In this paper, we examine the mixture regression model based on mixture of different type of distributions. In particular, we consider two-component mixture of normal-t distributions, and skew t-skew normal distributions. We obtain the maximum likelihood (ML) estimators for the parameters of interest using the expectation maximization (EM) algorithm. We give a simulation study and real data examples to illustrate the performance of the proposed estimators.

Matrix variate slash distribution

In this paper, we introduce a matrix variate slash distribution as a scale mixture of the matrix variate normal and the uniform distributions. We study some properties of the proposed distribution and give maximum likelihood (ML) estimators of its parameters using EM algorithm. We provide an iteratively reweighting algorithm to compute the ML estimates. Also, we give a small simulation study to show performance of the algorithm.

Parameter Estimation for Mixtures of Skew Laplace Normal Distributions and Application in Mixture Regression Modeling

ABSTRACT In this article, we propose mixtures of skew Laplace normal (SLN) distributions to model both skewness and heavy-tailedness in the neous data set as an alternative to mixtures of skew Student-t-normal (STN) distributions. We give the expectation–maximization (EM) algorithm to obtain the maximum likelihood (ML) estimators for the parameters of interest. We also analyze the mixture regression model based on the SLN distribution and provide the ML estimators of the parameters using the EM algorithm. The performance of the proposed mixture model is illustrated by a simulation study and two real data examples.

Joint Modelling of the Location, Scale and Skewness Parameters of the Skew Laplace Normal Distribution

In this article, we propose the joint location, scale and skewness models of the skew Laplace normal (SLN) distribution as an alternative model for the joint modelling location, scale and skewness models of the skew-t-normal distribution when the data set contains both asymmetric and heavy-tailed observations. We obtain the maximum likelihood estimators for the parameters of the joint location, scale and skewness models of the SLN distribution using the expectation–maximization algorithm. The performance of the proposed model is demonstrated by a simulation study and a real data example.

Doubly reweighted estimators for the parameters of the multivariate t-distribution

ABSTRACT The t-distribution (univariate and multivariate) has many useful applications in robust statistical analysis. The parameter estimation of the t-distribution is carried out using maximum likelihood (ML) estimation method, and the ML estimates are obtained via the Expectation-Maximization (EM) algorithm. In this article, we will use the maximum Lq-likelihood (MLq) estimation method introduced by Ferrari and Yang (2010) to estimate all the parameters of the multivariate t-distribution. We modify the EM algorithm to obtain the MLq estimates. We provide a simulation study and a real data example to illustrate the performance of the MLq estimators over the ML estimators.

Robust mixture regression modeling using the least trimmed squares (LTS)-estimation method

ABSTRACT Mixture regression models are used to investigate the relationship between variables that come from unknown latent groups and to model heterogenous datasets. In general, the error terms are assumed to be normal in the mixture regression model. However, the estimators under normality assumption are sensitive to the outliers. In this article, we introduce a robust mixture regression procedure based on the LTS-estimation method to combat with the outliers in the data. We give a simulation study and a real data example to illustrate the performance of the proposed estimators over the counterparts in terms of dealing with outliers.

Robust parameter estimation of regression model with AR(p) error terms

ABSTRACT In this article, we consider a linear regression model with AR(p) error terms with the assumption that the error terms have a t distribution as a heavy-tailed alternative to the normal distribution. We obtain the estimators for the model parameters by using the conditional maximum likelihood (CML) method. We conduct an iteratively reweighting algorithm (IRA) to find the estimates for the parameters of interest. We provide a simulation study and three real data examples to illustrate the performance of the proposed robust estimators based on t distribution.