Table 4.

 Linear regression model of potential predictors of endline math score

Characteristics	Model adjusted for baseline math score (n=3177)			Full model† (n=3169)
	Regression coefficient* (95% CI)	P value		Regression coefficient (95% CI)	P value
Baseline standardized mathematics score (SD)	0.59 (0.57 to 0.62)	<0.001		0.56 (0.53 to 0.59)	<0.001
Intervention group (control group as reference)
Voucher	0.04 (−0.05 to 0.14)	0.35		0.04 (−0.05 to 0.13)	0.42
Free glasses	0.11 (0.01 to 0.21)	0.03		0.10 (0.002 to 0.19)	0.04
Age (years)	−0.14 (−0.17 to −0.11)	<0.001		−0.14 (−0.17 to −0.11)	<0.001
Male sex	−0.02 (−0.07 to 0.04)	0.58		—	—
Wearing glasses at baseline	0.05 (−0.03 to 0.12)	0.25		—	—
Gansu residence	−0.17 (−0.25 to −0.08)	<0.001		−0.13 (−0.22 to −0.04)	0.003
Refractive error (≥−0.5 D to 0.5 D as reference):
≤−2 D	0.14 (−0.16 to 0.43)	0.37		—	—
−2 D to −0.5 D	0.10 (−0.21 to 0.40)	0.54		—	—
≥0.5 D	0.12 (−0.19 to 0.43)	0.45		—	—
One or both parents with ≥12 years of education‡	0.07 (0.008 to 0.13)	0.03		0.03 (−0.04 to 0.09)	0.40
Family wealth (poorest third as reference)§:
Middle third	0.06 (−0.01 to 0.13)	0.11		0.03 (−0.04 to 0.10)	0.38
Top third	0.07 (0.001 to 0.14)	0.05		0.01 (−0.06 to 0.08)	0.83
Boarding at school	0.05 (−0.03 to 0.14)	0.20		0.03 (−0.05 to 0.11)	0.49
Both parents out-migrated for work¶	0.02 (−0.07 to 0.11)	0.68		—	—

D=diopter.

*Except for regression coefficient for baseline math score (simple regression), coefficients for different variables are for multiple models with endline math score as dependent variable, adjusted for baseline math score.

†Including variables associated with endline math score P<0.20 in model also including baseline math score.

‡Data missing for seven students.

§Data missing for three students.

¶Data missing for eight students.