Subjects
A total of 6,010 (2,975 males and 3,035 females)[1] high-school students in Hong Kong
participated in the present study. The mean age was 14.35 years old with a standard
deviation of 3.13 years. Among the participants, 68.5 per cent (n ¼ 4,117) were aged
from 13 to 15; 31.1 per cent (n ¼ 1,869) from 16-18; and the remaining 0.4 per cent
(n ¼ 24) were unidentified.