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Submitted on: 20 October 2009.
Revised on: 11 November 2009.
Accepted on: 16 December 2009.
___________________Investigacion Economica---UNIV NACIONAL AUTONOMA MEXICO, FAC ECONOMIA
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Submitted on: 24 January 2003.
Revised on: 14 March 2003.
Accepted on: 10 May 2003.
___________________Investigacion Economica---UNIV NACIONAL AUTONOMA MEXICO, FAC ECONOMIA
Submitted on: 17 April 2013.
Revised on: 06 August 2013.
Accepted on: 28 August 2013.
___________________Investigacion Economica---UNIV NACIONAL AUTONOMA MEXICO, FAC ECONOMIA
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Submitted on: 16 October 2000.
Revised on: 16 January 2001.
Accepted on: 26 February 2001.
___________________Investigacion Economica---UNIV NACIONAL AUTONOMA MEXICO, FAC ECONOMIA
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Submitted on: 13 February 2009.
Revised on: 22 April 2009.
Accepted on: 08 May 2009.
___________________Investigacion Economica---UNIV NACIONAL AUTONOMA MEXICO, FAC ECONOMIA