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Table 1 Adjusted TRISS misclassification rate and adjusted w-statistic

From: Evaluation of trauma care using TRISS method: the role of adjusted misclassification rate and adjusted w-statistic

TRISS Method deaths Od survivors Os Expected:
Positive (P(s) < 50%) TP FP Ed = TP+FP
  a b Ed = a+b
  EOd Us Ed = Us+ EOd
Negative (P(s) > 50%) FN TN Es = FN+TN
  c = c1+c2 d Es = c+d
  c1 = Pd; EOs Es = Ud+EOs
  c2 = nonPd   
  Ud   
Observed: Od = TP+FN Os = FP+TN N = Ed+Es
  Od = a+c Os = b+d N = a+b+c+d
  Od = EOd+Ud Os = Us+EOs N = Od+Os
Misclassification rate = (FP + FN)/N = (b + c)/N = (Us + Ud)/N
Adjusted misclassification rate = (FP+FN-Pd)/N
   = (b +c -Pd)/N
   = Us + Ud - Pd/N
W statistic = (FP+TN) - (FN+TN)/N = (FP - FN)/N
   = (b+d) - (c+d)/N = (b-c)/N
   = (Os - Es)/N
   = (Us+EOs) - (Ud + EOs)/N = (Us - Ud)/N
Adjusted W statistic = [FP-(FN-nonPd)/N = (FP- Pd)/N
   = [b - (c - nonPd)]/N = (b - Pd)/N
   (c = c1+ c2; Pd = c - nonPd)
   = (Us - Pd)/N
   = [Os- (Es- nonPd)]/N
  1. Elements of TRISS misclassification rate and w-statistic, formulas and abbreviation used to describe observed and expected outcome Abbreviations: TP (a) = True positive = EOd = Expected observed deaths, FP (b) = False positive = Us= Unexpected survivors, FN (c) = False negative = Ud = Unexpected deaths, (c1) = Pd = preventable deaths, (c2) = nonPd = Nonpreventable deaths, TN (d) = True negative = EOs = Expected observed survivors, Ed= Expected deaths, Es = Expected survivors, Od = Observed deaths, Os = Observed survivors.