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/> [[alternative HTML version deleted]] ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
