Submitted on: 17 April 2000.
Revised on: 07 July 2000.
Accepted on: 23 August 2000.
___________________BMC Medical Research Methodology
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Submitted on: 11 November 2015.
Revised on: 09 January 2016.
Accepted on: 26 February 2016.
___________________BMC Medical Research Methodology
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Submitted on: 06 December 2005.
Revised on: 26 January 2006.
Accepted on: 11 February 2006.
___________________BMC Medical Research Methodology
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