Association of breast feeding with potentially confounding variables
| Variable | Number (total = 1580) | Breast fed (%) n = 1159 | Bottle fed (%) n = 421 | Age adjusted odds ratio* (95% CI) |
|---|---|---|---|---|
| *Odds ratios give odds of being breast fed in each strata of variable compared with reference stratum. †Trend per category of variable gives increase in odds ratio for each increase in category of ordinal variable (excluding unknown). | ||||
| Social class in childhood | ||||
| Non-manual | 202 | 76 | 24 | 1.00 (ref) |
| Manual | 1319 | 73 | 27 | 0.85 (0.60 to 1.20) |
| Unknown | 59 | 63 | 37 | 0.56 (0.30 to 1.05) |
| Birth order | ||||
| First | 486 | 70 | 30 | 1.00 (ref) |
| Second | 382 | 73 | 27 | 1.14 (0.85 to 1.54) |
| Third | 236 | 74 | 28 | 1.22 (0.86 to 1.74) |
| Fourth or more | 466 | 77 | 23 | 1.42 (1.06 to 1.90) |
| Unknown | 10 | 70 | 30 | 0.88 (0.22 to 3.49) |
| Trend per category of birth order† | 1.12 (1.02 to 1.23) | |||
| Father unemployed | ||||
| No | 745 | 72 | 28 | 1.00 (ref) |
| Yes | 587 | 76 | 24 | 1.13 (0.88 to 1.46) |
| Unknown | 248 | 69 | 31 | 0.81 (0.59 to 1.12) |
| Birth place | ||||
| Caerphilly | 793 | 73 | 27 | 1.00 (ref) |
| Other UK | 734 | 73 | 27 | 1.02 (0.81 to 1.28) |
| Outside UK | 51 | 88 | 12 | 2.50 (1.05 to 5.97) |
| Unknown | 2 | 100 | 0 | – |
| Social class in adulthood | ||||
| Non-manual | 539 | 75 | 25 | 1.00 (ref) |
| Manual | 1002 | 73 | 27 | 0.88 (0.69 to 1.12) |
| Unknown | 39 | 77 | 23 | 1.00 (0.46 to 2.17) |
| Smoking history | ||||
| Never | 428 | 71 | 29 | 1.00 (ref) |
| Ex smoker | 466 | 78 | 22 | 1.43 (1.06 to 1.95) |
| Current smoker | 680 | 72 | 28 | 1.02 (0.78 to 1.33) |
| Unknown | 6 | 83 | 17 | 2.02 (0.23 to 17.73) |
| Trend per category of smoking† | 0.99 (0.86 to 1.13) | |||
| Age at baseline examination | ||||
| 44 to 49 | 571 | 66 | 34 | 1.00 (ref) |
| 50 to 54 | 493 | 77 | 23 | 1.74 (1.33 to 2.29) |
| 55 + | 516 | 78 | 22 | 1.85 (1.41 to 2.43) |
| Trend per category of age† | 1.38 (1.20 to 1.58) | |||
| Mean (SD) | Age adjusted mean difference (95% CI) (breast minus bottle) | |||
| Birth weight, kg | 1079 | 3.74 (0.83) | 3.41 (0.88) | 0.32 (0.21 to 0.44) |