- Correspondence to Claudia Diaz Olavarrieta, National Institute of Public Health Research Center on Health Population, 7a Cerrada Fray Pedro de Gante # 50, Col. Seccion XVI, Tlalpan, Mexico City, 14000, Mexico;
- Received September 9, 2009
- Accepted February 22, 2010
- First published June 3, 2010.
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