1 Center for Policy, Outcomes and Prevention, Stanford University School of Medicine, 117 Encina Commons, Stanford, CA 94305, USA. Electronic address: cjwang1@stanford.edu.
2 Centre for Population Health Sciences, Lee Kong Chian School of Medicine, Nanyang Technological University, Singapore, Clinical Sciences Building, 11 Mandalay Road, Singapore 308232, Singapore. Electronic address: josip.car@ntu.edu.sg.
3 Department of Pediatrics, Boston University School of Medicine, 72 East Concord Street, Boston, MA 02118, USA. Electronic address: barry.zuckerman@bmc.org.