- Correspondence to Ricardo Pérez-Núñez, Centro de Investigación en SIstemas de Salud, Instituto Nacional de Salud Publica, Cuernavaca, Morelos CP 62100, México;
- Received October 9, 2019
- Revised March 26, 2020
- Accepted April 1, 2020
- First published April 25, 2020.
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