Table 1.

Demographic background of participants.

	Number	%
Gender
Male	2966	46.2
Female	3461	53.8
Age
13–15	3258	50.9
16–17	3139	49.1
Grade point average last semester
Excellent	154	2.4
Good	1562	24.4
Moderate	3079	48.2
Bad	1598	25.0
Ethnic group
Kinh	6211	96.2
Others	243	3.8
Father’s education
High school and lower	4584	72.5
Diploma and higher	1742	27.5
Mother’s education
High school and lower	4501	70.6
Diploma and higher	1879	29.4