Table 1.
Descriptive characteristics of the study sample.
| Variables | n | Mean | Median | SD | Range | Percent | ||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Child characteristics | ||||||||||||
| Child age at assessment (years) | 279 | 11.3 | 11.4 | 0.8 | 8.5–14.3 | |||||||
| Child sex (% girls) | 279 | 50.5 | ||||||||||
| Birth weight (kg) | 277 | 3.5 | 3.5 | 0.5 | 2.5–4.7 | |||||||
| Duration of gestation (weeks) | 279 | 39.1 | 39.0 | 1.5 | 35.0–44.0 | |||||||
| Adoption status (% adopted) | 279 | 16.5 | ||||||||||
| Breast-feeding status (% yes) | 272 | 74.6 | ||||||||||
| Caregiver characteristics/family environment | ||||||||||||
| Maternal age at delivery (years) | 279 | 23.8 | 22.9 | 5.7 | 15.0–42.0 | |||||||
| Parity before child’s birth | 279 | 2.0 | 2.0 | 1.8 | 0.0–9.0 | |||||||
| Marital status (% single) | 279 | 27.3 | ||||||||||
| Education (years of schooling) | 278 | 8.5 | 9.0 | 2.5 | 0.0–16.0 | |||||||
| Employment (% working) | 277 | 71.8 | ||||||||||
| SES scorea | 279 | 28.6 | 28.0 | 11.8 | 8.0–66.0 | |||||||
| Nonverbal reasoning abilityb | 279 | 34.9 | 37.0 | 9.8 | 4.0–56.0 | |||||||
| Language at interview (% primarily Inuktitut) | 279 | 9.3 | ||||||||||
| Residential crowding (no. of persons/room) | 277 | 1.5 | 1.3 | 0.5 | 0.5–3.8 | |||||||
| Food insecurity (% yes)c | 277 | 38.3 | ||||||||||
| Contaminants | ||||||||||||
| Cord Hg (μg/L) | 269 | 21.6 | 16.6 | 17.5 | 1.0–99.3 | |||||||
| Current Hg (μg/L) | 275 | 4.6 | 3.0 | 4.7 | 0.1–34.1 | |||||||
| Cord PCB-153 (μg/kg fat) | 268 | 123.1 | 93.6 | 100.5 | 9.7–653.6 | |||||||
| Current PCB-153 (μg/kg fat) | 274 | 73.7 | 45.9 | 83.2 | 3.5–809.5 | |||||||
| Cord Pb (μg/dL) | 269 | 4.7 | 3.7 | 3.3 | 0.8–20.9 | |||||||
| Current Pb (μg/dL) | 275 | 2.7 | 2.1 | 2.2 | 0.4–12.8 | |||||||
| Seafood nutrients | ||||||||||||
| Cord DHA (% phospholipids) | 264 | 3.7 | 3.5 | 1.3 | 1.1–7.7 | |||||||
| Current DHA (% phospholipids) | 274 | 2.4 | 2.2 | 1.0 | 0.1–5.5 | |||||||
| Cord Se (μg/L) | 252 | 339.5 | 276.4 | 173.7 | 110.5–1579.2 | |||||||
| Current Se (μg/L) | 275 | 197.4 | 181.6 | 94.8 | 71.1–947.5 | |||||||
| Other prenatal exposures | ||||||||||||
| Tobacco smoke (% yes) | 271 | 84.9 | ||||||||||
| Binge drinking of alcohol (% yes)d | 238 | 34.5 | ||||||||||
| Illicit drug use (% yes) | 240 | 30.0 | ||||||||||
| aAssessed with the Hollingshead index, which is computed from predefined scores given for parental occupation status and education (Hollingshead 1975). bBased on the Raven Progressive Matrices (Raven et al. 1992). cFood insecurity was defined as mother reporting having not enough food to eat for her family at least 1 day in the preceding month. dBinge drinking corresponds to consumption of ≥ 5 standard drinks per occasion; 1 standard drink corresponds to 0.5 oz of absolute alcohol, which is equivalent to 350 mL of beer (12 oz), 175 mL of wine (6 oz), or 44 mL of liquor (1.5 oz). | ||||||||||||