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Submitted on: 10 September 2003.
Revised on: 15 October 2003.
Accepted on: 24 November 2003.
___________________Economic Analysis and Policy---ELSEVIER
Submitted on: 29 November 2006.
Revised on: 17 January 2007.
Accepted on: 10 February 2007.
___________________Economic Analysis and Policy---ELSEVIER
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