Table 2. Mean values of refractive error (D) according to urinary cotinine level.

	Urinary cotinine level (ng/ml)
	T1	T2	T3	P for trenda
Model 1b	−3.10±0.22	−2.7±0.19	−2.16±0.17	0.001
Model 2c	−3.06±0.21	−2.64±0.18	−2.09±0.18	0.001
Model 3d	−3.08±0.21	−2.87±0.18	−2.04±0.18	<0.001

Abbreviation: D, diopter.

^aP-values were calculated by using analysis of covariance (ANCOVA) test and P for trend was obtained from general linear model.

^bModel 1 was unadjusted.

^cModel 2 was adjusted for age and sex.

^dModel 3 was adjusted for age, sex, area of residence, parental income level, receipt of basic livelihood security, physical activity, and serum 25-hydroxyvitamin D level. Values are shown as least-squared means±standard errors.