Table 1.

Mean serum cotinine concentrations and cognitive test scores for children and adolescents, 6–16 years of age, NHANES III (1988–1994).

Variable	Geometric mean serum cotinine level (ng/mL)	Math	Reading	Block design	Digit span
Total (n = 4,399)	0.23	94.6	92.5	9.6	8.7
Sex
Male	0.22	94.2	92.1	10.0##	8.6*
Female	0.24	95.0	92.9	9.2##	8.8*
Race/ethnicity
Non-Hispanic black	0.45##	86.5##	84.9##	7.1##	8.0##
Non-Hispanic white (referent)	0.22	97.6	95.6	10.3	9.1
Hispanic	0.14#	87.6##	86.3##	8.7##	7.5##
Non-Hispanic other	0.16	99.5	90.4	10.2	8.2**
Region
Midwest	0.32*	96.0	93.2	10.1	9.0*
South	0.28	93.0	91.8	8.9*	8.5
West	0.15	95.8	92.0	10.1*	8.7
Northeast (referent)	0.20	94.3	93.7	9.6	8.6
Parent marital status
Married	0.20##	96.1##	93.6##	9.8##	8.8##
Not married	0.41##	88.9##	88.1##	8.7##	8.2##
Parent education level
< High school graduate	0.39##	86.2##	83.6##	8.3##	7.7##
High school graduate	0.30##	92.8##	91.1##	9.2##	8.5##
> High school graduate (referent)	0.14	100.5	98.1	10.6	9.5
Poverty index ratio
Lower tercile	0.37##	87.8##	84.8##	8.4##	8.0##
Middle tercile	0.22*	94.3##	92.5##	9.5##	8.6##
Higher tercile (referent)	0.15	101.2	99.7	10.8	9.8
Lead
Lower tercile (referent)	0.16	97.7	96.2	9.9	9.0
Middle tercile	0.24 #	94.7**	92.3##	9.8	8.7*
Higher tercile	0.48##	87.7##	84.6##	8.5 ##	8.1##
Ferritin
Lower tercile (referent)	0.21	94.5	92.2	9.7	8.7
Middle tercile	0.23	94.9	92.9	9.7	8.8
Higher tercile	0.24	94.6	92.5	9.4	8.7
Smokinga
Prenatal and postnatal	1.48##	92.1**	87.5#	8.9##	8.5*
Prenatal only	0.14	92.0	93.9	10.1	8.8
Postnatal only	0.77##	92.0##	89.1##	9.1##	8.4##
None (ref)	0.10	96.5	92.6	10.2	9.1
Received care in NICUa
Yes	0.30	93.4	89.1	9.9	8.7
No	0.24	94.7	91.4	9.7	8.9
Birth weighta
< 2,500 g	0.41*	88.9#	87.2*	8.2##	8.1*
> 2,500 g	0.24*	95.0#	91.6*	9.9##	9.0*

A significant association is compared with the referent group. For bivariate categories the referent group for one category is the other group.

^aIncludes only children 6–11 years of age.

^*p ≤0.05;

^**p ≤0.01;

^#p ≤0.005;

^##p ≤0.001.