title: The effect of hospital care on early survival after penetrating trauma.
abstract: BACKGROUND
  The effectiveness of emergency medical interventions can be best evaluated using time-to-event statistical methods with time-varying covariates (TVC), but this approach is complicated by uncertainty about the actual times of death. We therefore sought to evaluate the effect of hospital intervention on mortality after penetrating trauma using a method that allowed for interval censoring of the precise times of death.
  
  
  METHODS
  Data on persons with penetrating trauma due to interpersonal assault were combined from the 2008 to 2010 National Trauma Data Bank (NTDB) and the 2004 to 2010 National Violent Death Reporting System (NVDRS). Cox and Weibull proportional hazards models for survival time (tSURV) were estimated, with TVC assumed to have constant effects for specified time intervals following hospital arrival. The Weibull model was repeated with tSURVinterval-censored to reflect uncertainty about the precise times of death, using an imputation method to accommodate interval censoring along with TVC.
  
  
  RESULTS
  All models showed that mortality was increased by older age, female sex, firearm mechanism, and injuries involving the head/neck or trunk. Uncensored models showed a paradoxical increase in mortality associated with the first hour in a hospital. The interval-censored model showed that mortality was markedly reduced after admission to a hospital, with a hazard ratio (HR) of 0.68 (95% CI 0.63, 0.73) during the first 30 min declining to a HR of 0.01 after 120 min. Admission to a verified level I trauma center (compared to other hospitals in the NTDB) was associated with a further reduction in mortality, with a HR of 0.93 (95% CI 0.82, 0.97).
  
  
  CONCLUSIONS
  Time-to-event models with TVC and interval censoring can be used to estimate the effect of hospital care on early mortality after penetrating trauma or other acute medical conditions and could potentially be used for interhospital comparisons.
authors.affiliation: Department of Surgery, Maine Medical Center, 887 Congress Street, Suite 210, Portland, 04102, ME, USA. clarkd@mmc.org.|Center for Outcomes Research and Evaluation, Maine Medical Center, Portland, 04101, ME, USA. clarkd@mmc.org.|Tufts University School of Medicine, Boston, 02111, MA, USA. clarkd@mmc.org.|Harvard Injury Control Research Center, Harvard School of Public Health, Boston, 02115, MA, USA. clarkd@mmc.org.
authors.forename: David E
authors.initials: DE
authors.lastname: Clark
authors.affiliation: Center for Outcomes Research and Evaluation, Maine Medical Center, Portland, 04101, ME, USA.
authors.forename: Peter C
authors.initials: PC
authors.lastname: Doolittle
authors.affiliation: Department of Surgery, Maine Medical Center, 887 Congress Street, Suite 210, Portland, 04102, ME, USA.|Tufts University School of Medicine, Boston, 02111, MA, USA.
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Winchell
authors.affiliation: Department of Biostatistics, Harvard School of Public Health, Boston, 02115, MA, USA.
authors.forename: Rebecca A
authors.initials: RA
authors.lastname: Betensky
keywords: Injury; Interval censoring; NTDB; NVDRS; Penetrating; Regression; Survival analysis; Time-to-event analysis; Time-varying covariates; Trauma