Demographic factors	Items	Number	%
Gender	Male	272	42.2
	Female	373	57.8
	Total	645	100
Age	15 - 16	17	2.7
	17	607	94.1
	18 - 20	21	3.3
	Total	645	100
Educational level	1^st year of senior secondary education	19	2.9
	2^nd year of senior secondary education	604	93.6
	3^rd year of senior secondary education	22	3.4
	Total	645	100
Father educational level	Primary education or less	21	3.3
	Junior secondary education	42	6.5
	Senior secondary education	57	8.8
	Undergraduate education	326	50.5
	Postgraduate education	199	30.9
	Total	645	100
Mother educational level	Primary education or less	20	3.1
	Junior secondary education	74	11.5
	Senior secondary education	99	15.3
	Undergraduate education	283	43.9
	Postgraduate education	169	26.2
	Total	645	100
Monthly income	RMB 5,000 or less	21	3.3
	RMB 5,001 - 10,000	93	14.4
	RMB 10,001 - 15,000	114	17.7
	RMB 15,001 - 20,000	164	25.4
	RMB 20,001 or above	253	39.2
	Total	645	100