- 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 31 January 2017
- Revised 3 April 2017
- Accepted 20 April 2017
- Published online 17 May 2017.
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