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Corresponding author at: Diagonal Paraguay 257, of 1501, 8330015 Chile. Tel.: +56 2 29783455; fax: +56 2 29783413. E-mail address: epuentes@fen.uchile.cl (E. Puentes).
This version of the paper has benefited with comments made by two anonymous referees and participants of the seminars at LACEA, PAA and University of Pennsylvania.
There are no conflicts of interest.
The authors thank reviewers on previous versions for useful comments and Grand Challenges Canada (Grant 0072-03), Bill & Melinda Gates Foundation (Global Health Grant OPP1032713), and the Eunice Shriver Kennedy National Institute of Child Health and Development (Grant R01 HD070993) for financial support.
© 2016 The Authors