1. Division of Biostatistics University of Minnesota Minneapolis Minnesota USA
2. Center for Design & Analysis Amgen Inc. Thousand Oaks California USA
3. The Center for Injury Research and Policy Abigail Wexner Research Institute at Nationwide Children's Hospital Columbus Ohio USA
4. Department of Mathematics Hong Kong Baptist University Kowloon Tong Hong Kong
5. Department of Biostatistics, Epidemiology and Informatics, The Perelman School of Medicine University of Pennsylvania Philadelphia Pennsylvania USA