Table 1.

Demographic information of participants

Variables	Groups	Cohort 1	Cohort 2	Cohort 3
Age in Wave 1	−	10.37±0.38	13.50±0.50	16.02±0.38
Gender	Female	48.3%	49.0%	56.3%
	Male	51.7%	51.0%	43.7%
Residence	City	50.5%	48.7%	51.5%
	Township	18.6%	21.9%	26.2%
	Rural region	30.9%	29.4%	23.3%
Only child	Yes	93.9%	96.9%	76.3%
	No	6.1%	3.1%	23.7%
Mother's education	< College	74.2%	90.5%	80.7%
	≧ College	25.8%	9.5%	19.3%
Father's education	< College	69.6%	89.3%	76.7%
	≧ College	30.4%	10.7%	23.3%
2018 Annual income	< ¥50,000	53.4%	73.8%	54.2%
	¥50,000–100,000	26.3%	15.7%	30.3%
	> ¥100,000	20.3%	10.5%	15.5%

Note. ¥ = CNY.