Submitted on: 04 March 2001.
Revised on: 25 May 2001.
Accepted on: 11 July 2001.
___________________Gaceta Sanitaria---ELSEVIER
Submitted on: 24 April 1999.
Revised on: 26 May 1999.
Accepted on: 16 June 1999.
___________________Gaceta Sanitaria---ELSEVIER
Submitted on: 01 January 1998.
Revised on: 27 January 1998.
Accepted on: 05 March 1998.
___________________Gaceta Sanitaria---ELSEVIER
Submitted on: 08 November 2009.
Revised on: 26 January 2010.
Accepted on: 27 March 2010.
___________________Gaceta Sanitaria---ELSEVIER
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Submitted on: 11 February 2021.
Revised on: 07 April 2021.
Accepted on: 01 June 2021.
___________________Gaceta Sanitaria---ELSEVIER