Table 2. Subgroup analysis of association between the EBV infection and OSCC risk.

Subgroup analysis	No. of Studies	Pooled ORs (95% CI) f	P value	I2 (%)	P value
					Heterogeneity	Meta-regression
Overall	13	5.03(1.80–14.01)	0.002	87	<0.001	-
Study location
Asia	5	4.17(0.69–25.21)	0.120	88	<0.001	0.244
Africa	3	1.96(0.24–15.91)	0.530	88	<0.001
Europe and USA	5	9.69(3.16–29.72)	<0.001	63	0.028
Economic level
Developing countries	6	3.83(0.94–15.53)	0.060	87	<0.001	0.678
Developed countries	7	6.92(1.35–35.40)	0.020	88	<0.001
Number of patients
<100	5	2.17(0.44–10.80)	0.342	92	<0.001	0.191
≥100	8	10.47(2.39–45.79)	0.002	83	<0.001
Publication year
Before 2000	6	4.25(0.99–18.29)	0.052	88	<0.001	0.801
2000 and After	7	6.17(1.27–29.95)	0.024	88	<0.001
Tissue type
PE a	9	2.39(0.78–7.33)	0.128	88	<0.001	0.033
Frozen/Fresh	4	31.27(5.79–169.01)	<0.001	64	0.038
Detection method b
PCR	8	3.37(0.90–12.65)	0.072	91	<0.001	0.507
Nested PCR	2	7.62(2.50–23.22)	<0.001	0	0.984
RT-qPCR	1	-		-	-
ISH	1	-		-	-
IHC	1	-		-	-
Detection index
EBV DNA c	11	4.36(1.42–13.40)	0.010	88	<0.001	0.533
EBV RNA and protein d	2	16.76(0.22–1276.16)	0.202	86	0.007
Control type
Randomly selected	2	4.78 (1.60–14.33)	0.005	0	0.756	0.653
Age-matched	2	10.37 (5.30–20.28)	<0.001	0	0.534
Other e	9	4.44(1.16–16.97)	0.029	88	<0.001
Language
Chinese	2	6.29(2.49–15.89)	<0.001	1	0.315	0.826
English	11	4.84(1.48–15.88)	0.009	89	<0.001

^a PE: paraffin-embedded

^b PCR: polymerase chain reaction, ISH: in situ hybridization, IHC: immunohistochemical, RT-qPCR: reverse transcription and quantitative real-time polymerase chain reaction

^c EBV DNA: Bam HIW, and EBV-determined nuclear antigens 2 (EBNA2)

^d EBV RNA: EBV-encoded small non-polyadenylated RNA 1 (EBER1)

^e other normal oral tissues neither randomly selected nor age-matched

^f Use fixed-effects model if I² <50% or P value for heterogeneity >0.10