- Correspondence to Francesca Mattei, CESP Centre for Research in Epidemiology and Population Health, 16 avenue Paul Vaillant Couturier, Villejuif Cedex 94807, France;
- Received July 9, 2015
- Revised January 22, 2016
- Accepted February 5, 2016
- First published February 23, 2016.
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