Table 2.

Estimates from the multilevel model applied to 60,986 IQ observations in 22,724 children.

		Estimate	95%CI		P
Fixed Part	Constant	89.9	80.2	99.5	<0.001
	Age	−0.8	−1.0	−0.6	<0.001
	Age2	0.4	0.3	0.5	<0.001
	Birth year	0.14	0.12	0.16	<0.001
	Age x Birth year	−0.014	−0.020	−0.010	<0.001
	Height Z-score if <0	1.4	0.7	2.1	<0.001
	Height Z-score if ≥0	0.3	0.001	0.5	0.049
	Sex
	Male (referent)	–	–	–
	Female	−1.6	−1.9	−1.4	<0.001
Random Part	Variance
Level 3: School	Constant	120.2	−28.9	269.4
	Age	0.06	−0.02	0.1
	Age2	0.01	−0.004	0.03
	Height Z-score if <0	0.6	−0.2	1.4
Random Part	Variance
Level 2: Individual	Constant	60.0	57.2	60.7
	Age	0.5	0.4	0.6
	Age2	0.07	0.06	0.08
	Covariance
	Constant, Age	0.8	0.6	1.0
	Constant, Age2	−0.09	−0.2	0.02
	Age, Age2	−0.2	−0.2	−0.1
Random Part	Variance
Level 1: Visit	School 1	26.1	25.1	27.0
	School 2	24.1	23.5	24.7
	School 3	30.9	28.7	33.2
	School 4	39.9	37.8	42.0
	School 5	38.0	36.3	39.7