Leping Li (li3@niehs.nih.gov), Biostatistics Branch, National 
Institute of Environmental Health Sciences, Research Triangle Park, 
North Carolina  27709, USA

Yu Liang (liangy3@niehs.nih.gov), Biostatistics Branch, National 
Institute of Environmental Health Sciences, Research Triangle Park, 
North Carolina  27709, USA

Robert Bass (bass1@niehs.nih.gov), Computational Biology Facility, National 
Institute of Environmental Health Sciences, Research Triangle Park, 
North Carolina  27709, USA
