Table 2. Subgroup analysis of the prevalence of ASB by quality of included studies, geographic regions, and the date of study conduction using Chi2 test for heterogeneity.

	Prevalence	95% CI	p-value	I2 (%)
Quality of included studies
High	0.06	0.02, 0.09	-	-
Intermediate	0.14	0.08, 0.21	0.001	99.3
Low	0.10	0.08, 0.13	0.001	89.0
Geographic region of Iran
North	0.13	0.09, 0.18	0.001	99.0
South	0.11	0.05, 0.16	0.001	95.1
Year of study conduction
1996–2005	0.14	0.06, 0.22	0.001	99.5
2005–2013	0.13	0.09, 0.17	0.001	94.6