- Correspondence to Magdalena Kozela, Chair of Epidemiology and Population Studies, Faculty of Health Sciences, Jagiellonian University Medical College, 20, Grzegorzecka St, Krakow 31–531, Poland;
- Received January 31, 2017
- Revised April 3, 2017
- Accepted April 20, 2017
- First published May 17, 2017.
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