title: Factors affecting the ambulance response times of trauma incidents in Singapore.
abstract: OBJECTIVE
  Time to definitive care is important for trauma outcomes, thus many emergency medical services (EMS) systems in the world adopt response times of ambulances as a key performance indicator. The objective of this study is to examine the underlying risk factors that can affect ambulance response times (ART) for trauma incidents, so as to derive interventional measures that can improve the ART.
  
  
  METHODS
  This was a retrospective study based on two years of trauma data obtained from the national EMS operations centre of Singapore. Trauma patients served by the national EMS provider over the period from 1 January 2011 till 31 December 2012 were included. ART was categorized into "Short" (<4min), "Intermediate" (4-8min) and "Long" (>8min) response times. A modelling framework which leveraged on both multinomial logistic (MNL) regression models and Bayesian networks was proposed for the identification of main and interaction effects.
  
  
  RESULTS
  Amongst the process-related risk factors, weather, traffic and place of incident were found to be significant. The traffic conditions on the roads were found to have the largest effect-the odds ratio (OR) of "Long" ART in heavy traffic condition was 12.98 (95% CI: 10.66-15.79) times higher than that under light traffic conditions. In addition, the ORs of "Long ART" under "Heavy Rain" condition were significantly higher (OR 1.58, 95% CI: 1.26-1.97) than calls responded under "Fine" weather. After accounting for confounders, the ORs of "Long" ART for trauma incidents at "Home" or "Commercial" locations were also significantly higher than that for "Road" incidents.
  
  
  CONCLUSIONS
  Traffic, weather and the place of incident were found to be significant in affecting the ART. The evaluation of factors affecting the ART enables the development of effective interventions for reducing the ART.
authors.affiliation: Health Services Research and Biostatistics Unit, Division of Research, Singapore General Hospital, 226 Outram Road, Singapore 169039, Singapore. Electronic address: lam.shao.wei@sgh.com.sg.
authors.forename: Sean Shao Wei
authors.initials: SS
authors.lastname: Lam
authors.affiliation: Health Services Research and Biostatistics Unit, Division of Research, Singapore General Hospital, 226 Outram Road, Singapore 169039, Singapore. Electronic address: nguyen.ngoc.hoang.long@sgh.com.sg.
authors.forename: Francis Ngoc Hoang Long
authors.initials: FN
authors.lastname: Nguyen
authors.affiliation: Medical Department, Singapore Civil Defence Force, 91 Ubi Ave 4, Singapore 408827, Singapore. Electronic address: ng_yih_yng@scdf.gov.sg.
authors.forename: Yih Yng
authors.initials: YY
authors.lastname: Ng
authors.affiliation: Health Services Research and Biostatistics Unit, Division of Research, Singapore General Hospital, 226 Outram Road, Singapore 169039, Singapore. Electronic address: vanessalpx@yahoo.com.sg.
authors.forename: Vanessa Pei-Xuan
authors.initials: VP
authors.lastname: Lee
authors.affiliation: Department of General Surgery, Singapore General Hospital; Health Services Research and Biostatistics Unit, Division of Research, Singapore General Hospital, 226 Outram Road, Singapore 169039, Singapore. Electronic address: wong.ting.hway@sgh.com.sg.
authors.forename: Ting Hway
authors.initials: TH
authors.lastname: Wong
authors.affiliation: Health Services Research and Biostatistics Unit, Division of Research, Singapore General Hospital, 226 Outram Road, Singapore 169039, Singapore. Electronic address: stephanie.fook.m.c@sgh.com.sg.
authors.forename: Stephanie Man Chung
authors.initials: SM
authors.lastname: Fook-Chong
authors.affiliation: Department of Emergency Medicine, Singapore General Hospital; Health Services Research and Biostatistics Unit, Division of Research, Singapore General Hospital; Health Services and Systems Research, Duke-NUS Graduate Medical School, 226 Outram Road, Singapore 169039, Singapore. Electronic address: marcus.ong.e.h@sgh.com.sg.
authors.forename: Marcus Eng Hock
authors.initials: ME
authors.lastname: Ong
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000552:Ambulances / Q000706:statistics & numerical data* / Q000600:supply & distribution; D001499:Bayes Theorem; D002648:Child; D004779:Environment Design / Q000706:statistics & numerical data; D005260:Female; D006801:Humans; D015994:Incidence; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D062072:Patient Acuity; D012189:Retrospective Studies; D012846:Singapore; D013996:Time and Motion Studies; D014887:Weather; D014947:Wounds and Injuries / Q000453:epidemiology* / Q000628:therapy*; D055815:Young Adult
keywords: Ambulance response time; Emergency medical services; Multinomial logistic regression; Trauma