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

Table 1 Adjusted TRISS 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

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.

ISSN: 1749-7922