| Surviving cohort at 45 years* | Surviving cohort at 42 years | ||||||
| Total | Participant | Not in 45-year sample | % Bias§ | Participant | % Bias¶ | ||
| n = 17 313 n (%) | n = 9377 n (%) | Refusal† n = 2840 n (%) | Other‡ n = 5096 n (%) | n = 11 419 n (%) | |||
| Demographic characteristics | |||||||
| Gender | |||||||
| Male | 8875 (51.3) | 4665 (49.8) | 1288 (45.3) | 2922 (57.4) | −2.9 | 5626 (49.3) | −3.9 |
| Female | 8439 (48.7) | 4712 (50.3) | 1553 (54.7) | 2174 (42.7) | 3.3 | 5793 (50.7) | 4.1 |
| Ethnicity | |||||||
| White | 15 245 (96.8) | 9186 (98.0) | 2525 (97.7) | 3534 (93.3) | 1.2 | 11 180 (97.9) | 1.1 |
| Non-white | 500 (3.2) | 188 (2.0) | 59 (2.3) | 253 (6.7) | −37.5 | 238 (2.1) | −34.4 |
| Social characteristics | |||||||
| Mother’s husband’s social class (birth) | |||||||
| Non-manual | 4226 (26.8) | 2498 (28.8) | 697 (26.0) | 1031 (23.3) | 7.5 | 2970 (28.1) | 5.2 |
| Manual | 11 092 (70.3) | 5979 (68.9) | 1901 (71.0) | 3212 (72.5) | −2.0 | 7342 (69.4) | −1.4 |
| No male head | 466 (3.0) | 197 (2.3) | 79 (3.0) | 190 (4.3) | −23.3 | 262 (2.5) | −13.8 |
| Mother’s duration of schooling (birth) | |||||||
| > Statutory age | 4102 (25.4) | 2389 (27.0) | 619 (22.7) | 1094 (24.0) | 6.3 | 2803 (26.0) | 2.8 |
| ⩽ Statutory age | 12 034 (74.6) | 6468 (73.0) | 2103 (77.3) | 3463 (76.0) | −2.1 | 7995 (74.0) | −0.9 |
| Housing tenure (7 year) | |||||||
| Owned | 6012 (42.3) | 3651 (44.5) | 954 (39.5) | 1407 (39.2) | 5.2 | 4274 (43.0) | 1.7 |
| Rented | 8190 (57.7) | 4552 (55.5) | 1459 (60.5) | 2179 (60.8) | −3.8 | 5675 (57.0) | −1.2 |
| Hospitalisation (7 year) | |||||||
| No | 7721 (54.4) | 4489 (54.8) | 1366 (56.7) | 1866 (51.8) | 0.7 | 5430 (54.7) | 0.6 |
| Yes | 6478 (45.6) | 3696 (45.2) | 1043 (43.3) | 1739 (48.2) | −0.9 | 4500 (45.3) | −0.7 |
| Period of social care (7 year) | |||||||
| No | 13 999 (97.8) | 8096 (98.1) | 2389 (98.1) | 3514 (96.8) | 0.3 | 9820 (98.0) | 0.2 |
| Yes | 320 (2.2) | 156 (1.9) | 47 (1.9) | 117 (3.2) | −13.6 | 196 (2.0) | −9.1 |
| Behavioural characteristics | |||||||
| Externalising behaviour (7 year) | |||||||
| Normal | 6459 (44.3) | 3927 (47.0) | 1124 (45.1) | 1408 (37.8) | 6.1 | 4695 (46.3) | 4.5 |
| Intermediate | 6226 (42.7) | 3528 (42.2) | 1063 (42.6) | 1635 (43.9) | −1.2 | 4285 (42.2) | −1.2 |
| Problem | 1890 (13.0) | 902 (10.8) | 307 (12.3) | 681 (18.3) | −16.9 | 1165 (11.5) | −11.5 |
| Internalising behaviour (7 year) | |||||||
| Normal | 7903 (54.2) | 4822 (57.7) | 1280 (51.3) | 1801 (48.4) | 6.5 | 5748 (56.7) | 4.6 |
| Intermediate | 4633 (31.8) | 2532 (30.3) | 833 (33.4) | 1268 (34.1) | −4.7 | 3123 (30.8) | −3.1 |
| Problem | 2039 (14.0) | 1003 (12.0) | 381 (15.3) | 655 (17.6) | −14.3 | 1274 (12.6) | −10.0 |
| Cognitive characteristics | |||||||
| Reading score (7 year) | |||||||
| Normal | 12 907 (89.0) | 7616 (91.2) | 2164 (87.4) | 3127 (85.0) | 2.5 | 9153 (90.5) | 1.8 |
| Low | 1603 (11.1) | 737 (8.8) | 312 (12.6) | 554 (15.1) | −20.7 | 959 (9.5) | −14.4 |
| Maths score (7 year) | |||||||
| Normal | 12 196 (86.0) | 7207 (87.9) | 2018 (83.4) | 2971 (83.2) | 2.2 | 8648 (87.2) | 1.4 |
| Low | 1988 (14.0) | 989 (12.1) | 401 (16.6) | 598 (16.8) | −13.6 | 1275 (12.9) | −7.9 |
| Physical characteristics | |||||||
| Birthweight | |||||||
| Normal | 15 169 (94.1) | 8350 (94.4) | 2540 (93.2) | 4279 (93.9) | 0.3 | 10 158 (94.2) | 0.2 |
| Low (<2500 g) | 957 (5.9) | 493 (5.6) | 186 (6.8) | 278 (6.1) | −5.1 | 631 (5.9) | −1.7 |
| Short stature (7 year) | |||||||
| No | 12 203 (91.6) | 7193 (92.9) | 2049 (90.7) | 2961 (89.5) | 1.4 | 8635 (92.1) | 0.5 |
| Yes | 1113 (8.4) | 554 (7.2) | 211 (9.3) | 348 (10.5) | −14.3 | 737 (7.9) | −6.0 |
| Overweight (7 year) | |||||||
| Not overweight | 11 634 (89.6) | 6845 (90.4) | 1924 (87.2) | 2865 (89.2) | 0.9 | 8224 (89.9) | 0.3 |
| Overweight | 1352 (10.4) | 724 (9.6) | 282 (12.8) | 346 (10.8) | −7.7 | 925 (10.1) | −2.9 |
| Maternal behaviour | |||||||
| Smoking after 4th month of pregnancy (birth) | |||||||
| No | 10 690 (66.9) | 5943 (67.7) | 1818 (67.4) | 2929 (64.8) | 1.2 | 7169 (67.0) | 0.3 |
| Yes | 5300 (33.2) | 2830 (32.3) | 878 (32.6) | 1592 (35.2) | −2.7 | 3526 (33.0) | −0.6 |
| Breastfeeding (7 year) | |||||||
| ⩾1 month | 6157 (43.5) | 3772 (46.2) | 924 (38.4) | 1461 (40.9) | 6.2 | 4414 (44.5) | 2.3 |
| <1 month | 7993 (56.5) | 4400 (53.8) | 1483 (61.6) | 2110 (59.1) | −4.8 | 5499 (55.5) | −1.8 |
*Excluding deaths by age 45 years. †Permanent refusals (n = 1038) and refusals to 45-year survey (n = 1802). ‡Group comprises emigrants (n = 1300), no contact attempted (n = 3004), and eligible non-response not classified as refusal (ie 3632 − 2840 = 792) at 45 years. §Percentage bias ((45-year sample% − total surviving cohort%)/total surviving cohort%); positive bias represents an overrepresentation of the characteristic in the sample relative to the total cohort, negative bias an underrepresentation). ¶Compared with total cohort excluding deaths by age 42 years (n = 17 438).