title: Intracluster correlation coefficient in multicenter childhood trauma studies.
abstract: OBJECTIVE
  To calculate the intracluster correlation coefficient (ICC) for emergency department (ED) shock rate, early trauma death (ie, death during the first 24 h after arrival at hospital), and in-hospital trauma death rate for multicenter childhood injuries.
  
  
  METHODS
  The National Trauma Data Bank (5th revision), the largest multicenter trauma registry in the US, was used. Data from 80 trauma centers were used to calculate the ICC for in-hospital trauma death rate. Thirty three states provided data for calculation of the ICC for ED shock and early trauma death rate.
  
  
  RESULTS
  From 2000 to 2004, 13% of the 952 242 patients in the National Trauma Data Bank were <15 years old. Approximately 17 000 of these children had injuries with an injury severity score >15, of whom 84% (14 095 subjects) were hospitalized at 80 level I or II trauma centers in 33 states. The ICCs for ED shock rate, early trauma death rate, and in-hospital death rate were 0.005 (95% CI 0.000 to 0.010), 0.014 (95% CI 0.004 to 0.024), and 0.023 (95% CI 0.013 to 0.033), respectively. These ICCs were calculated for boys and girls and also for blunt and penetrating injuries.
  
  
  CONCLUSIONS
  Clustered childhood trauma studies that aim to compare different aspects of pre-hospital and hospital trauma care should incorporate these ICCs for sample calculation. When cluster randomized clinical trials are mounted, if sample sizes are calculated without adjustment for ICC, then the planned trial is likely to be seriously underpowered.
authors.affiliation: University of Texas School of Public Health, Dallas Regional Campus, Dallas, Texas 75390-9128, USA. bahman.roudsari@utsouthwestern.edu
authors.forename: Bahman
authors.initials: B
authors.lastname: Roudsari
authors.forename: Raymond
authors.initials: R
authors.lastname: Fowler
authors.forename: Avery
authors.initials: A
authors.lastname: Nathens
mesh_terms: D000293:Adolescent; D017677:Age Distribution; D002648:Child; D002675:Child, Preschool; D016000:Cluster Analysis; D004636:Emergency Service, Hospital; D005260:Female; D017052:Hospital Mortality; D006801:Humans; D007231:Infant, Newborn; D008297:Male; D012042:Registries; D012774:Shock, Traumatic / Q000401:mortality*; D014193:Trauma Centers / Q000706:statistics & numerical data*; D015599:Trauma Severity Indices; D014481:United States / Q000453:epidemiology; D014947:Wounds and Injuries / Q000401:mortality*