Statistics Department, Stanford University, Stanford, California, USA.|Department of Microbiology & Immunology, Stanford University School of Medicine, Stanford, California, USA.|Statistics Department, Stanford University, Stanford, California, USA.|Statistics Department, Stanford University, Stanford, California, USA.|Department of Microbiology & Immunology, Stanford University School of Medicine, Stanford, California, USA.|Department of Microbiology & Immunology, Stanford University School of Medicine, Stanford, California, USA.|Statistics Department, Stanford University, Stanford, California, USA.