Table 2.

Pooled and subgroup analyses

Stratification	Number of study	Model		Heterogeneity statistics
		Fixed-effects model (RR, 95% CI)	Random-effects model (RR, 95% CI)	I 2	P value
Overall	13	1.162 (1.128-1.197)	1.152 (1.082-1.222)	40.2%	0.066
Geographic area
Europe	6	1.18 (1.09-1.27)	1.18 (1.09-1.27)	0%	0.450
North America	4	1.16 (1.12-1.20)	1.17 (1.00-1.34)	78.9%	0.003
Other	3	1.17 (1.08-1.25)	1.17 (1.08-1.25)	0%
Study population size
< 5000	8	1.21 (1.03-1.39)	1.23 (1.20-1.22)	21.7%	0.257
≥ 5000	5	1.16 (1.12-1.20)	1.14 (1.07-1.21)	63.1%	0.029
Publication year
1997-2005	6	1.01 (0.91-1.10)	1.01 (0.91-1.10)	0%	0.857
2006-2013	7	1.19 (1.15-1.22)	1.19 (1.15-1.23)	2.3%	0.408
Adjusted RR
Yes	5	1.16 (1.12-1.20)	1.14 (1.04-1.25)	67.9%	0.014
No	8	1.17 (1.09-1.25)	1.17 (1.06-1.28)	7.8%	0.370
Study population age (year)
≤ 10	7	1.16 (1.13-1.20)	1.17 (1.06-1.28)	64.5%	0.010
> 10	6	1.15 (1.07-1.23)	1.15 (1.07-1.23)	0%	0.692