Table 1.

Sample descriptive statistics

Variable	Category	Frequency	Percent
Gender	Male	684	46.9
	Female	775	53.1
Grade	7th	241	16.5
	8th	216	14.8
	9th	218	14.9
	10th	260	17.8
	11th	285	19.5
	12th	239	16.4
Ethnicity	Han ethnicity	1443	98.9
	Ethnic minorities	16	1.1
Province	Beijing	218	14.9
	Zhejiang	104	7.1
	Guangdong	98	6.7
	Henan	172	11.8
	Jiangxu	580	39.8
	Shanxi	105	7.2
	Sichuan	182	12.5