Check this out, this might help

 

http://arxiv.org/abs/0801.2934 

 

 

 

Ben Spycher

PhD student
Division of Clinical Epidemiology & Biostatistics

Institute of Social and Preventive Medicine
University of Berne
Finkenhubelweg 11 - CH-3012 Berne, Switzerland
Tel +41 31 631 35 07 / Fax +41 31 631 35 20
www.ispm.ch <http://www.ispm.ch/>  

 


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