Stevo Lukić1, Zarko Cojbašić2, Zoran Milošević3. 1. University of Niš, Medical Faculty, Niš, Serbia; University Clinical Center, Clinical Center Niš, Niš, Serbia. Electronic address: slukic@medfak.ni.ac.rs. 2. Faculty of Mechanical Engineering, University of Niš, Niš, Serbia. 3. University of Niš, Medical Faculty, Niš, Serbia; Department of Medical Statistic and Informatics, Institute of Public Health, Niš, Serbia.