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Table 1 Description of potential demographic, socioeconomic, and behavioral predictors of low IQ and unadjusted associations*

From: Early life determinants of low IQ at age 6 in children from the 2004 Pelotas Birth Cohort: a predictive approach

Characteristic Rate n (%) Low IQ n (%) Unadjusted OR (95% CI)
All 3523 (100) 594 (16.9)  
Mother’s and father’s skin color (n = 3518)    p = 0.0000
White mother and father or either one 2736 (77.8) 373 (13.6) 1
Non-white mother and father 782 (22.2) 219 (28.0) 2.5 (2.0–3.0)
Teenage parents (n = 3522)    p = 0.0007
Neither 2776 (78.8) 436 (15.7) 1
Both or either one 746 (21.2) 157 (21.1) 1.4 (1.2–1.8)
Mother with a partner (n = 3522)    p = 0.0069
No 556 (15.8) 116 (20.9) 1.4 (1.1–1.7)
Yes 2966 (84.2) 477 (16.1) 1
Father employed at the child’s birth (n = 3445)    p = 0.0000
No 590 (17.1) 155 (26.3) 2.1 (1.7–2.6)
Yes 2855 (82.9) 412 (14.4) 1
Mother employed between pregnancy and the child’s first 12 months of life (n = 3456)    p = 0.0000
No 1645 (47.6) 359 (21.8) 2.0 (1.7–2.4)
Employed either during pregnancy or the child’s first 12 months of life 1811 (52.4) 220 (12.2) 1
Household income at the child’s birth (n = 3522)    p = 0.0000
One or less than one monthly minimum wage 823 (23.4) 248 (30.1) 7.6 (5.3–11.1)
Up to 2 monthly minimum wages 1041 (29.6) 213 (20.5) 4.5 (3.1–6.6)
Up to 4 monthly minimum wages 1004 (28.5) 97 (9.7) 1.9 (1.3–2.8)
More than 4 monthly minimum wages 654 (18.6) 35 (5.4) 1
Maternal education (years of schooling) (n = 3490)    p = 0.0000
0–4 527 (15.1) 197 (37.4) 9.4 (7.1–12.4)
5–8 1458 (41.8) 306 (21.0) 4.2 (3.3–5.3)
9 or more 1505 (43.1) 90 (6.0) 1
Number of siblings at the child’s birth (n = 3522)    p = 0.0000
Two or less 3149 (89.4) 454 (14.4) 1
Three or more 373 (10.6) 139 (37.3) 3.5 (2.8–4.4)
Number of persons per room at age 12 months (n = 3423)    p = 0.0000
<3 1687 (49.3) 190 (11.3) 1
≥3 1736 (50.7) 384 (22.1) 2.2 (1.9–2.7)
Maternal level of physical activity during and after pregnancy (n = 3522)    p = 0.0000
Physically inactive 2844 (80.8) 535 (18.8) 2.5 (1.9–3.3)
Active either during or after pregnancy 678 (19.2) 58 (8.6) 1
Maternal and paternal smoking during pregnancy (n = 3522)    p = 0.0000
None 1982 (56.3) 242 (12.2) 1
At least one parent smoked 1540 (43.7) 351 (22.8) 2.1 (1.7–2.8)
Maternal smoking during the child’s first year of life (n = 3404)    p = 0.0000
No 2336 (68.6) 330 (14.1) 1
Smoked 1068 (31.4) 247 (23.1) 1.8 (1.5–2.2)
Number of father-child activities at age 12 months (n = 3424)    p = 0.0008
0–2 568 (16.6) 117 (20.6) 1.8 (1.3–2.5)
3–6 2288 (66.8) 387 (16.9) 1.4 (1.1–1.9)
7 activities** 568 (16.6) 70 (12.3) 1
Childcare during the first year of life (n = 3523)    p = 0.0008
No 3353 (95.2) 580 (17.3) 2.3 (1.3–4.1)
Yes 170 (4.8) 14 (8.2) 1
  1. *Logistic regression analysis in children age 6. The 2004 Pelotas Birth Cohort Study.
  2. **Score estimated from the mother’s reports of the father spending time with the child feeding, diapering, bathing soothing during bedtime, playing, tending or strolling.
  3. CI = confidence intervals; OR = odds ratios; IQ = intelligence quotient.