Table 2. Subgroup analyses in subset of included studies according to baseline characteristics for overall survival.

	HR	95%CI	Heterogeneity (%)	P	No. of included studies
Total	0.58	0.45 to 0.76	26.6	0.207	9
Study quality
Quality score<7	0.62	0.44 to 0.89	27.5	0.228	6
Quality score≤7	0.53	0.31 to 0.91	42.3	0.177	3
Research region
USA	0.52	0.42 to 0.66	3.2	0.401	6
Non-USA	1.21	0.57 to 2.54	0	0.606	3
Research center
Single	0.76	0.52 to 1.11	14.3	0.323	6
Multicenter	0.46	0.35 to 0.61	0	0.890	3
Sample size
≥400	0.58	0.40 to 0.82	24.8	0.256	5
≥400	0.61	0.38 to 1.00	46.2	0.134	4
First inclusion year
Before 2000	0.60	0.45 to 0.82	21.9	0.269	6
After 2000	0.52	0.27 to 1.03	53.3	0.118	3

CI= confidence intervence; DM: diabetes mellitus; HR= hazard ratios.