Table 1.

Descriptive Statistics

Theoretical Variables	Empirical Counterparts	Mean	SD	Within-twin SD/ overall SD
(1)	(2)	(3)	(4)	(5)
eH	Early health shocks (dummy)	0.09	0.28	0.35
IH	Health investment (¥/year)	225.83	772.00	0.62
IC	Educational investment (¥/year)	910.44	1225.73	0.20
θH	Height (cm)	137.33	19.30	0.13
	Weight (kg)	33.60	11.82	0.16
	BMI	17.39	3.22	0.27
	General health statusa	2.92	0.63	0.34
θC	Literature (score: 1–100)	81.93	13.79	0.42
	Literature (relative measure)b	3.53	0.84	0.48
	Mathematics (score: 1–100)	80.90	16.41	0.43
	Mathematics (relative measure)b	3.48	0.92	0.50
	Good Student Awards (dummy)	0.24	0.43	0.51
	Awards in contests (dummy)	0.07	0.25	0.49
	Grade repetition (dummy)	0.04	0.21	0.52
	Doing minor actions in classc	1.73	0.76	0.49
	Always feel lonelyd	1.20	0.50	0.34
	Easily distractedd	1.59	0.68	0.34
	Easily frightenedd	1.37	0.60	0.28
	Emotionally unstabled	1.12	0.35	0.28
T	Paternal labor supply (days/month)	25.51	4.68
	Maternal labor supply (days/month)	25.32	4.72
c	Paternal consumption (¥/6 months)	700.33	869.38
	Maternal consumption (¥/6 months)	283.81	736.59
ω	Birth weight (kg)	2.46	0.47	0.36
ξ	Male	0.49	0.50	0.50
	Age	11.19	3.09
	Born at the first parity	0.79	0.40
h	Maternal age	36.85	4.84
	Maternal ethnicity (Han=1)	0.86	0.35
	Maternal schooling years	8.65	3.28
w, pI	Maternal working sector (Public=1)	0.08	0.27
	Rural	0.53	0.50
Y	Household asset (score)	−0.05	1.73

Note: The sample includes 1,456 pairs of twins. Column (5) presents the share of the within-twin standard deviation out of the overall sample standard deviation.

^a4-point Likert scale: 1 (worst) to 4 (best)

^b1 (top quintile in the class) to 5 (lowest quintile)

^c4-point Likert scale: 1 (never) to 4 (always)

^d3-point Likert scale: 1 (disagree), 2 (agree), 3 (strongly agree)