Table 2. Observed deaths/Expected deaths ratio and AUC of the three tools for 30-day and 90-day mortality.

O/E ratio = observed deaths/expected deaths; AUC = area under the curve; Std. Error = standard error; CI = confidence interval; Pre-op = preoperative; Post-op = postoperative; NELA = National Emergency Laparotomy Audit; P-POSSUM = Portsmouth Physiological and Operative Severity Score for the enumeration of Mortality and Morbidity

	Observed deaths	Expected deaths	O/E ratio	AUC	Std. error	P-value	95% CI
							Lower bound	Upper bound
30-day mortality
Pre-op NELA	10.4	3.2	3.25	0.791	0.033	<0.001*	0.727	0.855
Pre-op P-Possum	10.4	3.7	2.81	0.784	0.032	<0.001*	0.721	0.848
Post-op NELA	10.4	4.8	2.17	0.761	0.032	<0.001*	0.699	0.824
90-day mortality
Pre-op NELA	14.2	3.2	4.43	0.765	0.029	<0.001*	0.708	0.821
Pre-op P-Possum	14.2	3.7	3.84	0.749	0.029	<0.001*	0.692	0.807
Post-op NELA	14.2	4.8	2.96	0.745	0.028	<0.001*	0.691	0.800