Submitted on: 07 September 1998.
Revised on: 06 October 1998.
Accepted on: 05 November 1998.
___________________Journal of Intellectual Disabilities
Submitted on: 09 June 2001.
Revised on: 21 July 2001.
Accepted on: 06 September 2001.
___________________Journal of Intellectual Disabilities
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Submitted on: 04 April 2003.
Revised on: 01 June 2003.
Accepted on: 13 June 2003.
___________________Journal of Intellectual Disabilities