Submitted on: 18 December 1999.
Revised on: 05 January 2000.
Accepted on: 12 January 2000.
Stata Journal
Submitted on: 15 June 2013.
Revised on: 06 July 2013.
Accepted on: 21 July 2013.
Stata Journal
Submitted on: 22 March 2006.
Revised on: 20 April 2006.
Accepted on: 10 May 2006.
Stata Journal---SAGE PUBLICATIONS INC
Submitted on: 11 June 1998.
Revised on: 22 June 1998.
Accepted on: 04 July 1998.
Stata Journal
Submitted on: 26 April 2022.
Revised on: 27 May 2022.
Accepted on: 08 June 2022.
Stata Journal---SAGE PUBLICATIONS INC
http://reply.papertrans.cn/3/287/28607/28607-26.png
Submitted on: 15 March 2015.
Revised on: 21 April 2015.
Accepted on: 09 May 2015.
Stata Journal
http://reply.papertrans.cn/3/287/28607/28607-28.png
Submitted on: 11 February 2014.
Revised on: 02 March 2014.
Accepted on: 30 March 2014.
Stata Journal
Submitted on: 10 February 2013.
Revised on: 22 March 2013.
Accepted on: 13 April 2013.
Stata Journal