Table 2.

Subgroup analysis for the association between programmed death ligand 1 (PD-L1) expression and overall survival (OS)

Subgroup	Number of studies	Pooled HR(95%CI)	P value	Heterogeneity		Heterogeneity between groups (p value)
				I²	p value
Detection index						0.003
protein	9	1.30 (1.13–1.48)	<0.001	0.473	0.056
mRNA	6	1.05 (1.00–1.09)	0.041	0.4	0.139
Detection method						0.007
immunofluorescence	2	1.12(0.88–1.41)	0.36	0.786	0.031
immunohistochemistry	7	1.39(1.18–1.64)	<0.001	0.269	0.224
RNA-sequencing	4	1.04(1.00–1.09)	0.045	0.172	0.305
other	2	1.24(0.91–1.69)	0.176	0.703	0.066
Race						0.51
asian	8	1.12 (1.01–1.25)	0.032	0.602	0.014
caucasian	7	1.21 (1.00–1.46)	0.049	0.482	0.072
Sample size						0.083
<100	7	1.34 (1.07–1.68)	0.012	0.415	0.114
≥100	8	1.08 (1.00–1.18)	0.05	0.476	0.064
Source of HR						0.038
Kaplan-Meier	5	1.21(1.07–1.38)	0.003	0	0.461
Cox regression	10	1.05(1.01–1.12)	0.021	0.626	0.004
Cutoff						0.001
protein staining percentage	7	1.45 (1.22–1.74)	<0.001	0.244	0.242
mRNA expression level	4	1.13 (1.00–1.27)	0.043	0.255	0.259
other	4	1.04 (0.99–1.09)	0.094	0.523	0.098
Year of publication						0.006
<2019	9	1.22(1.10–1.35)	<0.001	0.376	0.118
≥2019	6	1.04(1.00–1.09)	0.073	0.574	0.039

Heterogeneity between the groups reveals that detection index, detection method, source of hazard ratio (HR), cutoff and year of publication are the sources of significant heterogeneity (P < 0.05); however, race and sample size are not (P > 0.05).