Submitted on: 24 February 2006.
Revised on: 01 April 2006.
Accepted on: 24 April 2006.
___________________American Economic Journal-Applied Economics
Submitted on: 02 April 2018.
Revised on: 06 June 2018.
Accepted on: 05 July 2018.
___________________American Economic Journal-Applied Economics
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Submitted on: 26 September 1999.
Revised on: 25 October 1999.
Accepted on: 11 November 1999.
___________________American Economic Journal-Applied Economics
http://reply.papertrans.cn/1/13/1257/1257-35.png
Submitted on: 06 April 2020.
Revised on: 26 July 2020.
Accepted on: 24 August 2020.
___________________American Economic Journal-Applied Economics