Table 1.
Sample characteristics and relations of control variables to IQ score.
| Characteristic | Total n | Mean ± SD | Range | n (%) | Relation to IQ score (r) |
|---|---|---|---|---|---|
| Primary caregiver | |||||
| SESa | 282 | 28.4 ± 11.7 | 8.0–66.0 | ||
| Years of education | 282 | 8.5 ± 2.5 | 0.0–16.0 | ||
| Social environment compositeb | 282 | –0.02 ± 0.8 | –2.5–2.3 | 0.29** | |
| Marital status (married) | 282 | 124 (44.0) | 0.11# | ||
| Fluent in English or French | 282 | 256 (90.8) | 0.10# | ||
| Pregnancy history | |||||
| Maternal age at delivery | 282 | 24.0 ± 5.9 | 15.0–42.0 | 0.04 | |
| Parity | 282 | 2.0 ± 1.8 | 0.0–9.0 | –0.04 | |
| Alcohol during pregnancy (yes) | 241 | 70 (29.0) | 0.09 | ||
| Smoking during pregnancy (cigarettes/day) | 269 | 8.7 ± 7.3 | 0.0–50.0 | –0.14* | |
| Marijuana during pregnancy (days/month) | 239 | 0.4 ± 1.0 | 0.0–3.4 | –0.03 | |
| Child | |||||
| Age at assessment | 282 | 11.3 ± 0.8 | 8.6–14.3 | 0.08 | |
| Sex (female) | 282 | 143 (50.7) | 0.23** | ||
| Adopted | 282 | 47 (16.7) | –0.06 | ||
| Transported by plane | 282 | 98 (34.8) | –0.08 | ||
| WISC-IV scores | |||||
| Estimated Full Scale IQ score | 282 | 91.9 ± 11.7 | 61.0–125.0 | ||
| Perceptual Reasoning Index | 282 | 94.2 ± 11.2 | 61.0–127.0 | ||
| Working Memory Index | 282 | 89.5 ± 11.6 | 56.0–132.0 | ||
| Processing Speed Index | 282 | 86.6 ± 12.2 | 59.0–118.0 | ||
| Estimated Verbal Comprehension Index | 276 | 84.5 ± 15.1 | 38.8–116.9 | ||
| Exposure to contaminants | |||||
| Prenatal | |||||
| Cord blood mercury (μg/L) | 279 | 21.8 ± 17.5 | 1.0–99.3 | ||
| Maternal hair mercury (μg/g) | 70 | 4.9 ± 2.8 | 1.4–15.1 | ||
| Cord plasma PCB-153 (ng/g lipid) | 278 | 120.3 ± 95.0 | 9.7–653.6 | ||
| Cord blood lead (μg/dL) | 279 | 4.8 ± 3.4 | 0.8–20.9 | ||
| Current | |||||
| Blood mercury (μg/L) | 278 | 4.7 ± 4.7 | 0.1–34.1 | ||
| Hair mercury (μg/g) | 277 | 6.9 ± 6.5 | 0.3–45.0 | ||
| Plasma PCB-153 (ng/g lipid) | 276 | 73.5 ± 82.9 | 3.5–809.5 | ||
| Blood lead (μg/dL) | 278 | 2.7 ± 2.3 | 0.4–12.8 | ||
| Nutrient intake | |||||
| Prenatal | |||||
| Cord plasma DHA (% fatty acids) | 274 | 3.6 ± 1.2 | 1.1–7.7 | ||
| Cord blood selenium (μg/L) | 262 | 336.3 ± 181.4 | 112.1–1579.2 | ||
| Current | |||||
| Plasma DHA (% fatty acids) | 277 | 2.4 ± 1.0 | 0.1–5.5 | ||
| Blood selenium (μg/L) | 278 | 199.6 ± 91.3 | 67.9–947.5 | ||
| aHollingshead (2011). bBased on socioeconomic status, caregiver years of education, Peabody Picture Vocabulary Test raw score, Raven Progressive Matrices raw score, which were converted to standard scores and averaged. Pearson correlations with IQ were 0.26 for socioeconomic status, 0.12 for caregiver education, 0.32 for Peabody Vocabulary, and 0.19 for the Raven. *p < 0.05. **p < 0.001. #p < 0.10. | |||||