Table 2. Summary of meta-analyses.

	Risk factor	Blood transfusion	Tumour	Obesity	Diabetes	Tobacco use
Case number	RF+SSI+	39	226	720	229	340
	RF+SSI−	998	3924	28 717	5330	13 645
	RF− SSI+	1075	769	531	1314	938
	RF− SSI−	62 830	44 733	36 398	62 893	54 500
Meta-analysis	LogOR	0.94	0.8	0.58	0.53	0.36
	OR	2.55	2.23	1.79	1.7	1.43
	SE	0.17	0.09	0.12	0.15	0.07
	z	5.57	8.8	5.07	3.5	5.54
	P value	<0.001	<0.001	<0.001	<0.001	<0.001
Heterogeneity test	I2	0.00%	0.00%	67.56%	64.07%	0.00%
	Q (df)	0.17 (3)	1.34 (4)	11.58 (4)	21.13 (7)	5.78 (5)
	P value	0.983	0.85	0.02	<0.001	0.33
Leave-one-out sensitivity	lowest LogOR	0.88	0.7	0.54	0.44	0.32
	Highest LogOR	0.96	0.86	0.66	0.64	0.43
Egger’s publication bias	β	0.09	0.05	1.79	−1.21	0.76
	SE	1.08	0.81	7.6	0.89	0.73
	z	0.08	0.06	1.12	−1.35	0.91
	P value	0.934	0.95	0.263	0.178	0.363

The presenting data of the tumour were after exclusions of outliers.

I² refers, Heterogeneity index; RF+, exposure to the risk factor; RF−, no exposure to the risk factor; SSI, surgical site infections; SSI+, SSI positive; SSI−, SSI negative.