Table 2.

The prevalence of ROP based on region, gender, provinces and quality of studies

Variable		Studies (Na)	Sample (N)	Heterogeneity		95% CIb	Prevalence (%)
				I2	P-Value
Region	Center	20	12,355	93.65	< 0.001	21.8 to 28.4	24.9
	East	4	302	57.79	0.07	17 to 33	24.1
	North	12	2626	97.09	< 0.001	15.9 to 37.1	25
	South	4	2586	98.60	< 0.001	9.2 to 37.1	20.5
	West	2	131	0	0.67	7.6 to 19.1	12.3
	Test for subgroup differences: Q = 9.67, df(Q) = 4, P = 0.046
Gender	Boys	11	1467	92.65	< 0.001	11.9 to 28.5	18.9
	Girls	11	1184	85.02	< 0.001	12.8 to 25.4	18.3
	Rate ratio of boys to girls: ORc = 1.07(0.86 to 1.33, P = 0.501)
Provinces	Khozestan	1	576	0	–	28.3 to 35.9	32
	Mazandaran	8	1678	95.77	< 0.001	23.5 to 48.2	34.8
	Isfahan	4	1600	92.48	< 0.001	16.5 to 35	24.6
	Golestan	1	89	0	–	2.3 to 12.8	5.6
	Kerman	1	83	0	–	20.3 to 39.6	29
	Kermanshah	3	84	0	–	7.4 to 22.1	13.1
	Razavi Khorasan	3	219	67.89	0.044	12.4 to 34.2	21.3
	Guilan	1	310	0	–	16.5 to 25.5	20.9
	Kurdistan	1	47	0	–	4.5 to 23.1	10.6
	Semnan	1	270	0	–	0.4 to 3.4	1.1
	Fars	3	2010	99.09	< 0.001	4 to 50.8	17.2
	East Azarbaijan	2	549	91.32	0.001	4.6 to 25	11.3
	Tehran	14	10,407	91.32	< 0.001	25.1 to 31	28
	Zanjan	1	78	0	–	0.2 to 8.5	1.2
	Test for subgroup differences: Q = 97.59, df(Q) = 13, P < 0.001
Quality	Medium	20	7760	63.68	< 0.001	16.6 to 28.0	23.5
	High	22	10,240	96.65	< 0.001	19.1 to 28.7	23.5
	Test for subgroup differences: Q = 0, df(Q) = 1, P = 0.995

^aNumber

^bConfidence interval