Selahattin Kaçıranlar

On the almost unbiased generalized liu estimator and unbiased estimation of the bias and mse

In this paper, we derive the almost unbiased generalized Liu estimator and examine an exact unbiased estimator of the bias and mean squared error of the feasible generalized Liu estimator . We compare the almost unbiased generalized Liu estimator (AUGLE) with the generalized Liu estimator (GLE) and with the ordinary least squares estimator (OLSE).

COMBINING THE LIU ESTIMATOR AND THE PRINCIPAL COMPONENT REGRESSION ESTIMATOR

In this paper we introduce a class of estimators which includes the ordinary least squares (OLS), the principal components regression (PCR) and the Liu estimator [1]. In particular, we show that our new estimator is superior, in the scalar mean-squared error (mse) sense, to the Liu estimator, to the OLS estimator and to the PCR estimator.

The Restricted and Unrestricted Two-Parameter Estimators

In this article, we introduce a new two-parameter estimator by grafting the contraction estimator into the modified ridge estimator proposed by Swindel (1976). This new two-parameter estimator is a general estimator which includes the ordinary least squares, the ridge, the Liu, and the contraction estimators as special cases. Furthermore, by setting restrictions Rβ = r on the parameter values we introduce a new restricted two-parameter estimator which includes the well-known restricted least squares, the restricted ridge proposed by Groß (2003), the restricted contraction estimators, and a new restricted Liu estimator which we call the modified restricted Liu estimator different from the restricted Liu estimator proposed by Kaçıranlar et al. (1999). We also obtain necessary and sufficient condition for the superiority of the new two-parameter estimator over the ordinary least squares estimator and the comparison of the new restricted two-parameter estimator to the new two-parameter estimator is done by the criterion of matrix mean square error. The estimators of the biasing parameters are given and a simulation study is done for the comparison as well as the determination of the biasing parameters.

On the performance of two parameter ridge estimator under the mean square error criterion

Lipovetsky and Conklin [12] proposed an estimator, two parameter ridge (ridge-2) estimator, as an alternative to the ordinary least squares (OLS) and the ordinary ridge (ridge-1) estimators in the presence of multicollinearity. Lipovetsky [13] improved the two parameter model and investigated various characteristics of ridge-2 solutions. In this paper, we compare ridge-2 estimator with the OLS, ridge-1 and contraction estimators with respect to matrix mean square error (MSE) criterion. A numerical example from the literature has been analyzed to evaluate the performance of mentioned estimators in the theoretical results.

More on the restricted ridge regression estimation

Several alternative methods for derivation of the restricted ridge regression estimator (RRRE) are provided. Theoretical comparison and relationship of RRRE with related methods for regression with the multicollinearity problem are described. We also find inter-connections among RRRE, ordinary ridge regression estimator (ORRE), restricted least squares estimator (RLSE), modified ridge regression estimator (MRRE) and restricted modified generalized ridge estimator (RMGRE). Finally, numerical comparison, in addition to theoretical derivation, is also conducted with a Monte Carlo simulation and a real data example.

A Prediction-Oriented Criterion for Choosing the Biasing Parameter in Liu Estimation

The estimation of biasing parameter k in ridge regression is an important problem. There are many procedures in the literature for choosing k. For predictive performance, methods for selecting k were given. One of which is choosing k so as to minimize the PRESS statistic for ordinary ridge regression (Montgomery and Friedman, 1993). Liu (1993) introduced a new biased estimator which depends on the biasing parameter d and gave some estimates of d by analogy with the estimates of k. In this article, we propose and investigate PRESS statistic for selecting d and we also give a numerical example based on widely analyzed data set on Portland cement to illustrate the results.

On the Restricted Liu Estimator in the Logistic Regression Model

The logistic regression model is used when the response variables are dichotomous. In the presence of multicollinearity, the variance of the maximum likelihood estimator (MLE) becomes inflated. The Liu estimator for the linear regression model is proposed by Liu to remedy this problem. Urgan and Tez and Mansson et al. examined the Liu estimator (LE) for the logistic regression model. We introduced the restricted Liu estimator (RLE) for the logistic regression model. Moreover, a Monte Carlo simulation study is conducted for comparing the performances of the MLE, restricted maximum likelihood estimator (RMLE), LE, and RLE for the logistic regression model.

A Comparison of Mixed and Ridge Estimators of Linear Models

The presence of autocorrelation in errors and multicollinearity among the regressors has undesirable effects on the least squares regression. There are a wide range of methods, such as the mixed estimator or the ridge estimator, for estimating regression equations, which are aimed to overcome the usefulness of the ordinary least squares estimator or the generalized least squares estimator. The purpose of this article is to examine multicollinearity and autocorrelation problems simultaneously and, to compare the mixed estimator to the ridge regression estimator (RRE) by the dispersion and mse matrix criterions in the linear regression model with correlated or heteroscedastic errors.

The Almon two parameter estimator for the distributed lag models

ABSTRACT The two parameter estimator proposed by Özkale and Kaçıranlar [The restricted and unrestricted two parameter estimators. Comm Statist Theory Methods. 2007;36(15):2707–2725] is a general estimator which includes the ordinary least squares, the ridge and the Liu estimators as special cases. In the present paper we introduce Almon two parameter estimator based on the two parameter estimation procedure to deal with the problem of multicollinearity for the distiributed lag models. This estimator outperforms the Almon estimator according to the matrix mean square error criterion. Moreover, a numerical example and a Monte Carlo simulation experiment are presented by using different estimators of the biasing parameters.

Evaluation of the Predictive Performance of the Liu Estimator

Multiple linear regression models are frequently used in predicting (forecasting) unknown values of the response variable y. In this case, a regression model ability to produce an adequate prediction equation is of prime importance. This paper discusses the predictive performance of the Liu estimator compared to ordinary least squares, as well as to two other popular biased estimators, principal components and Ridge regression estimators. The theoretical results are illustrated by a numerical example, and a region is established where the Liu estimator is uniformly superior to the other three estimators.