表 1. Incidence of NSSI among male and female middle school students of different grades (n=3382).
Demographic characteristic | n | NSSI/case (%) | χ 2 | P |
Gender | 35.436 | <0.001 | ||
Male | 1678 | 747 (44.52) | ||
Female | 1704 | 933 (54.75) | ||
Grade | 620.472 | <0.001 | ||
Seventh grade | 1157 | 374 (32.32) | ||
Eighth grade | 1142 | 432 (33.82) | ||
Ninth grade | 1083 | 874 (80.70) |