Table 1. Characteristics of the 22,108 surveyed primary school students and their informants from 8 provinces in China.

Demographic characteristics of the children
age in years, mean(sd)	9.3 (1.8)
male, n(%)	11863 (53.7%)
urban resident, n(%)	11431 (51.7%)
Relationship between informant and the childa
mother, n(%)	10725 (48.5%)
father, n(%)	8996 (40.7%)
grandparent, n(%)	1200 (5.4%)
other relative, n(%)	959 (4.4%)

^a In 200 cases the relationship between the informant and child was unspecified.