The odd power cauchy family of distributions: properties,regression models and applications

We study some mathematical properties of a new generator of continuous distributions with one extra parameter called the odd power Cauchy family including asymptotics, linear representation, moments, quantile and generating functions, entropies, order statistics and extreme values. We introduce two bivariate extensions of the new family. The maximum likelihood method is discussed to estimate the model parameters by means of a Monte Carlo simulation study. We define a new log-odd power Cauchy–Weibull regression model. The usefulness of the proposed models is proved empirically by means of three real data sets.     

Quality of Life in College Students with and without Social Phobia

Prior studies demonstrating quality of life impairment in phobia and anxiety disorders have relied upon epidemiological samples or clinical data. Using the same quality of life scale, the Short Form 36-item Health Survey (SF-36), in Iranian college students allowed us to study the impact of social phobia (SP) on quality of life among the college students. This report summarizes findings from a cross sectional study on Iranian students with social phobia studying at Shahed University. Quality of life was measured using the Short Form 36-item Health Survey (SF-36) which is a widely used and valid questionnaire to measure quality of life in cross-sectional and longitudinal studies. Three standard instruments were used to measure social phobia severity, namely Social Phobia Inventory, Social Interaction Anxiety Scale, and Brief version of the Fear of Negative Evaluation Scale. The sample consisted of 202 college students, 72 with SP and 130 without SP. The main finding of this study was that students with social phobia reported significantly lower quality of life, particularly in general health (P = 0.02), vitality (P < 0.0001), social functioning (P < 0.0001), role functioning—emotional (P < 0.0001), and Mental health (P = 0.001) dimensions. Standardized summed scores for mental health components of the SF-36 showed that 36.2% of all the s with SP were severely impaired while 16.0% of the students in control croup were severely impaired. Findings demonstrated that Iranian socially anxious college students reported extensive functional disability, and lower well-being compared to those without SP. These findings should encourage education officers to implement systematic efforts to prevent and treat social anxiety among students.     

Predictive analysis for joint progressive censoring plans: a Bayesian approach

Comparative lifetime experiments are of particular importance in production processes when one wishes to determine the relative merits of several competing products with regard to their reliability. This paper confines itself to the data obtained by running a joint progressive Type-II censoring plan on samples in a combined manner. The problem of Bayesian predicting failure times of surviving units is discussed in details when parent populations are exponential. Two real data sets are analyzed in order to illustrate all the inferential procedures developed here. When destructive experiments under a censoring scheme finished, the researchers are usually interested to estimate remaining lifetimes of surviving units for sequel experiments. Findings of this paper are useful for these purposes specially when samples are non-homogeneous such as those taken from industrial storages.     

EM algorithm for mixture of skew-normal distributions fitted to grouped data

Grouped data are frequently used in several fields of study. In this work, we use the expectation-maximization (EM) algorithm for fitting the skew-normal (SN) mixture model to the grouped data. Implementing the EM algorithm requires computing the one-dimensional integrals for each group or class. Our simulation study and real data analyses reveal that the EM algorithm not only always converges but also can be implemented in just a few seconds even when the number of components is large, contrary to the Bayesian paradigm that is computationally expensive. The accuracy of the EM algorithm and superiority of the SN mixture model over the traditional normal mixture model in modelling grouped data are demonstrated through the simulation and three real data illustrations. For implementing the EM algorithm, we use the package called ForestFit developed for R environment available at https://cran.r-project.org/web/packages/ForestFit/index.html.     

The importance of sector‐stereotypical images in relation to job pursuit intentions

This study broadens the concept of employer image and demonstrates the relevance of applicants’ sector image when looking for employment in either nonprofit or for‐profit organizations. We apply the Stereotype Content Model to conceptualize image through perceived competence and warmth and use multilevel analyses on data from final‐year Master’s students. Results show the importance of the sector‐stereotypical image and are partially in line with our hypotheses. Job pursuit intentions for specific organizations are predicted by both the organizations’ as well as the respective sectors’ perceived warmth and competence. Pursuit intentions for the for‐profit sector are predicted only by the image of that sector. However, the intention to pursue employment in the nonprofit sector is predicted by both its competence and warmth as well as by the perceived warmth of its organizations. These findings are discussed in view of a trickle‐down effect and compared to previous findings on sector image among consumers.     

Iran’s Multi-ethnic Mosaic: A 23-Year Perspective

In this study, we embark on measuring inequality in Iran. We compute three measures of group-based inequality (Group-weighted Coefficient of Variation, Group-weighted Gini, and Group-weighted Theil) for the following outcomes: education, assets, income, and expenditure per capita. The groups are defined based on gender, ethnicity/language (Persian, Azeri, and other ethnic minorities), and region (urban versus rural and capital city versus other places) using 23 years of annual Household Expenditure and Income Surveys from 1990 through 2012. Inequality between groups based on religion (Muslim, non-Muslim), citizenship (Iranian, non-Iranian) are also studied using the 2006 census. Our analysis of the trend of horizontal inequality reveals substantial reduction in between-group inequalities over the 1990–2012 period. Yet, gender based income inequality remains high. The implications and underlying reasons for these results are discussed.

     

Correction to: Iran’s Multi-ethnic Mosaic: A 23-Year Perspective

Social Indicators Research - The article Iran’s Multi-ethnic Mosaic: A 23-Year Perspective, written Mahdi Majbouri and Sanaz Fesharaki, was originally published electronically on the...     

Efficiency of the QR class estimator in semiparametric regression models to combat multicollinearity

There are some classes of biased estimators for solving the multicollinearity among the predictor variables in statistical literature. In this research, we propose a modified estimator based on the QR decomposition in the semiparametric regression models, to combat the multicollinearity problem of design matrix which makes the data to be less distorted than the other methods. We derive the properties of the proposed estimator, and then, the necessary and sufficient condition for the superiority of the partially generalized QR-based estimator over partially generalized least-squares estimator is obtained. In the biased estimators, selection of shrinkage parameters plays an important role in data analysing. We use generalized cross-validation criterion for selecting the optimal shrinkage parameter and the bandwidth of the kernel smoother. Finally, the Monté-Carlo simulation studies and a real application related to bridge construction data are conducted to support our theoretical discussion.     

An Optimality Probability Index for Correlated Multiple Responses

In the real problems, there are many cases which have correlated quality characteristics so multiple response optimization can be more realistic if we can consider correlation structure of responses. In this study we propose a new method which uses multivariate normal probability to find the optimal treatment in an experimental design. Moreover, a heuristic method is used to find better factors’ level in all possible combinations in the designs with large number of controllable factors and their levels. Some simulated numerical examples and a real case were studied by the proposed approach and the comparison of the results with previous methods show efficiency of the proposed method.     

Nonparametric estimation of the entropy using a ranked set sample

This article is concerned with nonparametric estimation of the entropy in ranked set sampling. Theoretical properties of the proposed estimator are studied. The proposed estimator is compared with the rival estimator in simple random sampling. The applications of the proposed estimator to the mutual information estimation as well as estimation of the Kullback–Leibler divergence are provided. Several Monté-Carlo simulation studies are conducted to examine the performance of the estimator. The results are applied to the longleaf pine (Pinus palustris) trees and the body fat percentage datasets to illustrate applicability of theoretical results.