Table 1.
Characteristics of study population according to cognitive ability at age three.
| Average/Above Cognitive Ability | Below Average Cognitive Ability |
||||
|---|---|---|---|---|---|
| Valid | Total | n (%) | n (%) | p-Value | |
| 6362 (89.2) | 772 (10.8) | ||||
| Maternal Characteristics | |||||
| Age in first year of life * | 7134 | ||||
| N, Mean (sd) | 7134 | 6362, 31.6 (5.3) | 772, 31.0 (5.7) | 0.002 | |
| Partner in household in first year | 7134 | ||||
| No | 1099 | 934 (14.7) | 165 (21.4) | <0.001 | |
| Current Smoker | 7134 | ||||
| Yes | 1917 | 1642 (25.8) | 275 (35.6) | <0.001 | |
| Depression | |||||
| N, Mean (SD) | 7030 | 6276, 2.46 (3.60) | 754, 3.00 (4.20) | <0.001 | |
| Sociodemographic Characteristics | |||||
| Maternal Education | 7132 | ||||
| Lower Secondary | 1343 | 1104 (17.4) | 239 (31.0) | ||
| Upper Secondary | 1758 | 1547 (24.3) | 211 (27.3) | ||
| Sub Degree | 2053 | 1877 (29.5) | 176 (22.8) | ||
| Third Level and higher | 1978 | 1832 (28.8) | 146 (18.9) | <0.001 | |
| Income Quintile | 6576 | ||||
| Lowest | 1315 | 1113 (19.0) | 202 (28.3) | ||
| 2nd | 1314 | 1150 (19.6) | 164 (22.9) | ||
| 3rd | 1344 | 1195 (20.4) | 149 (20.8) | ||
| 4th | 1398 | 1286 (21.9) | 112 (15.7) | ||
| Highest | 1205 | 1117 (19.1) | 88 (12.3) | <0.001 | |
| Household Social Class | 6431 | ||||
| Professional/Managerial | 3391 | 3107 (49.0) | 284 (37.1) | ||
| Non-Manual/Skilled Manual | 2364 | 2108 (33.3) | 256 (33.4) | ||
| Semi-skilled/Unskilled Manual | 676 | 571 (9.0) | 105 (13.7) | ||
| Never Worked—no class defined | 672 | 551 (8.7) | 121 (15.8) | <0.001 | |
| Infant Characteristics | |||||
| Gender | 7134 | ||||
| Male | 3617 | 3140 (49.4) | 477 (61.8) | ||
| Female | 3517 | 3222 (50.6) | 295 (38.2) | <0.001 | |
| Birth weight | 7062 | ||||
| <2500 g | 408 | 354 (5.6) | 54 (7.0) | ||
| 2500–4000 g | 5655 | 5049 (80.2) | 606 (79.0) | ||
| >4000 g | 999 | 892 (14.2) | 107 (14.0) | 0.283 | |
| Gestational age in weeks ^ | 7119 | ||||
| N, mean (sd) | 6347, 39.5 (2.1) | 772, 39.5 (2.3) | 0.400 | ||
| Admission to NICU at birth | 7127 | ||||
| Yes | 976 | 857 (13.5) | 119 (15.4) | 0.141 |
* Maternal age includes n = 532 participants aged 40 or older who were coded as age 40 in original dataset. ^ Gestational age includes n = 10 participants with a gestational age of 25 weeks or less was recorded as 25.