[1] Duke Univ, Duke Univ Emergency Med, Durham, NC 27710 USA
[2] Minist Home Affairs, Home Team Med Serv Div, Singapore, Singapore
[3] Tan Tock Seng Hosp, Emergency Dept, Singapore, Singapore
[4] Natl Univ Singapore Hosp, Emergency Med Dept, Singapore, Singapore
[5] Singapore Gen Hosp, Dept Emergency Med, Singapore, Singapore
[6] Singapore Gen Hosp, Unit Prehosp Emergency Care, Singapore, Singapore
[7] Duke Univ, Duke Univ Biostat & Bioinformat, Durham, NC 27710 USA
[8] Duke Natl Univ Singapore, Hlth Serv & Syst Res, Med Sch, Singapore, Singapore