Modified maximum likelihood estimator under the Jones and Faddy's skew t-error distribution for censored regression model.

It is well-known that classical Tobit estimator of the parameters of the censored regression (CR) model is inefficient in case of non-normal error terms. In this paper, we propose to use the modified maximum likelihood (MML) estimator under the Jones and Faddy's skew t-error distribution, which covers a wide range of skew and symmetric distributions, for the CR model. The MML estimators, providing an alternative to the Tobit estimator, are explicitly expressed and they are asymptotically equivalent to the maximum likelihood estimator. A simulation study is conducted to compare the efficiencies of the MML estimators with the classical estimators such as the ordinary least squares, Tobit, censored least absolute deviations and symmetrically trimmed least squares estimators. The results of the simulation study show that the MML estimators work well among the others with respect to the root mean square error criterion for the CR model. A real life example is also provided to show the suitability of the MML methodology.

Evaluation of surface water quality characteristics by using multivariate statistical techniques: a case study of the Euphrates river basin, Turkey.

The surface water quality of the Euphrates river basin in Turkey are evaluated by using the multivariate statistical techniques known as factor analysis (FA) and multidimensional scaling (MDS) analysis. When FA was applied to the water quality data obtained from the 15 different surface water quality monitoring stations, two factors were identified, which were responsible from the 86.02% of the total variance of the water quality in the Euphrates river basin. The first factor called the urban land use factor explained 44.20% of the total variance and the second factor called the agricultural use factor explained 41.81% of the total variance. MDS technique showed that electrical conductivity (EC), percent sodium (Na%) and total salt are the most important variables causing difference in the water quality analysis.

Effects of physical environment on the stress levels of hemodialysis nurses in Ankara Turkey.

This study has been planned and executed as a field study for identifying the effect of physical environment on the stress levels of hemodialysis nurses who work in the official and private hemodialysis centers in the capital city of Turkey, Ankara (n=161). According to the results obtained from the study, it has been seen that "education level" and "institution of employment" of the hemodialysis nurses are significantly related with the stress levels of the hemodialysis nurses. Nurses' age, marital status, number of children, occupational seniority, years of working, employment status, husbands' occupation and husbands' educational levels are not significantly related with their stress levels.