1. Department of Psychosomatic Medicine and Psychotherapy, Riga Stradiņš University, LV-1046 Riga, Latvia
2. Statistics Unit, Riga Stradiņš University, LV-1048 Riga, Latvia
3. Institute of Life Sciences and Technology, Daugavpils University, LV-5401 Daugavpils, Latvia
4. Department of Public Health and Epidemiology, Riga Stradiņš University, LV-1010 Riga, Latvia