Table 5.

Prevalence of ROP among subjects with different birth weights.

Birth weight (g)	χ2	P
≤1000/1000–1500	18.183	<0.0071
≤1000/1500–2000	54.194	<0.0071
≤1000/2000–2500	122.887	<0.0071
1000~1500/1500–2000	35.230	<0.0071
1000~1500/2000–2500	78.365	<0.0071
1500~2000/2000–2500	18.789	<0.0071

(P=0.05/[n(n−1)/2+1]; n – number of groups=4; P=0.0071); ROP – retinopathy of prematurity.