Table 3.

Linear effects of the relationship between hair mercury level and 355 children’s neurodevelopmental outcomes

	Linear effect of hair Hg (μg/g) on outcomea		Test of departure from linearity (μg/g)b
	β (se)	p-value	p-value
Wechsler Intelligence Scale for Children (WISC-III)
Full-Scale IQ	0.11 (2.13)	0.96	0.18
Verbal	0.35 (2.22)	0.87	0.10
Performance	−1.14 (2.33)	0.63	0.52
Wechsler Individual Achievement Test (WIAT)
Reading Composite	−0.35 (2.31)	0.88	0.46
Basic Reading	1.01 (2.32)	0.66	0.52
Reading Comprehension	−3.79 (2.16)	0.08	0.52
Mathematics Composite	−0.04 (2.12)	0.98	0.06
Math Reasoning	0.25 (1.85)	0.89	0.03
Numerical Operations	−0.49 (2.12)	0.82	0.18
Wide Range Assessment of Visual Motor Ability (WRAVMA)
Visual-Motor Composite	1.32 (2.24)	0.56	0.03
Drawing	0.96 (2.18)	0.66	0.22
Matching	2.03 (2.29)	0.38	0.11
Pegboard	−0.13 (2.70)	0.96	0.06
Wide Range Assessment of Memory and Learning (WRAML)
General Memory Index	3.72 (2.56)	0.15	0.46
Wisconsin Card Sorting Test (WCST)
Perseveration errors	1.03 (2.49)	0.67	0.06
Stroop Test of Color-word Interference	0.80 (1.01)	0.43	0.38
Trail-Making Test
Time to complete Part B (transformed)c	0.06 (0.09)	0.50	0.50
Finger Tapping
Mean of 5 trials with dominant hand	0.82 (1.25)	0.51	0.10

^aModels were adjusted for gender, child age (6–7, 8–9, 10–11), race (white, Hispanic, black, other/missing), primary caregiver education (< high school, high school, college+), marital status (married or living as married/single, separated, divorced or widowed) as well as birthweight, socio-economic status, caregiver IQ, and blood lead, as smoothed variables. All smoothed variables were modeled with four degrees of freedom.

^bModels adjusted for all covariates above. Hair Hg level was included as a smoothed variable.

^cThe log transform of the Trail-Making Test Part B was used to normalize this variable.