Table 2.
Mean IQ, educational attainment, and monthly income at 30 years with respect to confounding variables
| Breastfeeding at 6 months | IQ | Educational attainment (years) | Monthly income (R$) | ||
|---|---|---|---|---|---|
| Maternal education at delivery, years | p<0·0001† | p<0·0001* | p<0·001* | p<0·0001* | |
| 0–4 | 359/1110 (32%) | 92·2 (91·5–92·9) | 9·2 (9·0–9·4) | 997 (931–1062) | |
| 5–8 | 417/1518 (27%) | 97·5 (97·0–98·1) | 11·1 (11·0–11·3) | 1356 (1281–1430) | |
| 9–11 | 98/378 (26%) | 103·2 (102·1–104·3) | 13·2 (12·9–13·5) | 1871 (1679–2063) | |
| ≥12 | 178/483 (37%) | 108·6 (107·7–109·5) | 15·3 (15·1–15·6) | 2846 (2614–3078) | |
| Family income, multiple of 1982 minimum wage | p=0·03† | p<0·0001* | p<0·0001* | p<0·0001* | |
| ≤1 | 209/684 (31%) | 91·5 (90·7–92·4) | 8·9 (8·6–9·1) | 940 (855–1024) | |
| 1·1–3 | 509/1722 (30%) | 96·6 (96·0–97·1) | 10·7 (10·6–10·9) | 1255 (1191–1320) | |
| 3·1–6 | 189/684 (28%) | 102·0 (101·2–102·9) | 13·1 (12·8–13·4) | 1894 (1750–2038) | |
| 6·1–10 | 69/204 (34%) | 106·7 (105·2–108·2) | 14·5 (14·1–14·9) | 2583 (2260–2907) | |
| >10 | 72/183 (39%) | 110·4 (108·9–112·0) | 15·8 (15·3–16·2) | 3208 (2787–3628) | |
| Birthweight, g | p<0·0001* | p<0·0001* | p<0·0001* | p<0·0001* | |
| <2500 | 57/247 (23%) | 94·4 (92·8–96·1) | 10·5 (10·0–11·0) | 1190 (1009–1370) | |
| 2500–2999 | 227/833 (27%) | 95·7 (94·8–96·5) | 10·6 (10·4–10·9) | 1266 (1161–1370) | |
| 3000–3499 | 407/1315 (31%) | 98·5 (97·8–99·1) | 11·4 (11·2–11·7) | 1538 (1444–1632) | |
| ≥3500 | 363/1097 (33%) | 99·9 (99·2–100·6) | 11·9 (11·6–12·1) | 1709 (1597–1821) | |
| Sex | p=0·88† | p=0·02† | p<0·0001† | p<0·0001† | |
| Male | 504/1677 (30%) | 98·5 (97·9–99·1) | 10·9 (10·7–11·1) | 1917 (1826–2008) | |
| Female | 550/1816 (30%) | 97·5 (96·9–98·1) | 11·7 (11·5–11·9) | 1104 (1034–1173) | |
Data are n/N (%) or mean (95% CI) unless stated otherwise. IQ=intelligence quotient.
*
Test for linear trend.
†
Test for heterogeneity.