TABLE I.

Summary Table of Bivariate Associations of Covariates with Mortality and Treatment Group

	Treatment Group Means and Proportions (± SD)*					P Value
	t0 (N = 1759)	t1 (N = 540)	t2 (N = 359)	t3 (N = 272)	t4 (N = 139)	Association with Treatment	Association with Mortality
Covariates (Wm)†
Glasgow Coma Scale score	12.67 ± 4.22	12.69 ± 4.14	11.66 ± 4.75	10.77 ± 5.13	9.68 ± 5.20	<0.001	<0.001
New Injury Severity Score	27.35 ± 8.97	27.21 ± 8.33	29.20 ± 9.62	32.31 ± 11.39	34.68 ± 14.05	<0.001	<0.001
Maximum Abbreviated Injury Score, head/neck region	1.71 ± 1.65	1.76 ± 1.69	2.01 ± 1.68	2.32 ± 1.83	2.50 ± 1.94	<0.001	<0.001
Cardiac comorbidity	0.13 ± 0.34	0.17 ± 0.37	0.20 ± 0.40	0.28 ± 0.45	0.27 ± 0.45	<0.001	0.002
Number of serious associated extremity injuries	1.65 ± 0.94	1.42 ± 0.73	1.54 ± 0.86	1.67 ± 1.01	1.68 ± 0.96	<0.001	<0.001
Arrival between 6 a.m. and 12 p.m.	0.24 ± 0.43	0.07 ± 0.26	0.20 ± 0.40	0.18 ± 0.39	0.22 ± 0.42	0.001	0.04
Age	31.86 ± 13.73	33.12 ± 15.73	34.25 ± 15.87	34.44 ± 16.33	33.38 ± 15.05	0.01	0.01
Bilateral fracture	0.02 ± 0.14	0.00 ± 0.06	0.01 ± 0.12	0.02 ± 0.12	0.02 ± 0.15	0.03	0.03
Teaching hospital	0.56 ± 0.50	0.67 ± 0.47	0.58 ± 0.50	0.53 ± 0.50	0.63 ± 0.49	0.38	0.15
Hospitals from Northeast region	0.08 ± 0.27	0.10 ± 0.30	0.09 ± 0.29	0.11 ± 0.32	0.07 ± 0.26	0.54	0.00
Treated at level-1 trauma center	0.39 ± 0.49	0.39 ± 0.49	0.45 ± 0.50	0.45 ± 0.50	0.48 ± 0.50	0.69	0.05
Cerebrovascular comorbidity	0.00 ± 0.04	0.00 ± 0.04	0.01 ± 0.08	0.00 ± 0.06	0.00 ± 0.00	0.74	0.01
Mortality (95% confidence interval)	3.7% (2.3% to 5.4%)	1.9% (0.7% to 3.3%)	4.2% (2.2% to 6.4%)	4.4% (2.3% to 6.7%)	4.3% (0.8% to 8.2%)

^*SD = standard deviation. Treatment groups are defined as t₀ (twelve hours or less), t₁ (more than twelve hours to twenty-four hours), t₂ (more than twenty-four hours to forty-eight hours), t₃ (more than forty-eight hours to 120 hours), and t₄ (more than 120 hours).

^†W_m = subset of covariates with bivariate associations with mortality (p < 0.2).