- Correspondence to Dr Abdulrahman M El-Sayed, Department of Epidemiology, Mailman School of Public Health, Columbia University, 722 W. 168th Street, R521, New York, NY 10032, USA;
- Received January 27, 2013
- Revised March 13, 2013
- Accepted March 14, 2013
- First published April 9, 2013.
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