Association between breast feeding and socioeconomic variables, Boyd-Orr cohort, UK
| No in subset with complete data for adjusted analyses* | Infant feeding status | Odds ratio (95% CI) | |||
|---|---|---|---|---|---|
| Variable | Breast fed | Bottle fed | Adjusted for age† | Adjusted for age† and survey district | |
| Odds ratios calculated using logistic regression with standard errors adjusted for clustering at the family level. | |||||
| *Odds ratios were calculated on the same subset of subjects with full data for the index explanatory variable and all covariates adjusted for, in order to ensure an unbiased assessment of confounding. | |||||
| †Age entered as a continuous variable. | |||||
| ‡Number of children entered as a continuous variable. | |||||
| §Income (shillings; s) per head per week as recorded in original survey, but with the original last three groups collapsed into a single category. | |||||
| ¶Shillings and pence per head per week spent on food as recorded in the original survey but with the original last three groups collapsed into a single category. | |||||
| ¶Assigned using the Registrar General’s 1931 classification of occupations from social class I (professional) to social class V (unskilled manual). | |||||
| Mean (SD) no of children‡ | 2987 | 4.6 (2.0) | 4.6 (2.2) | 0.99 (0.92 to 1.06) | 0.96 (0.89 to 1.03) |
| p=0.72 | p=0.23 | ||||
| Birth order (%) | 2994 | ||||
| 1 | 479 (70.8) | 198 (29.3) | 1.00 | 1.00 | |
| 2 | 517 (73.5) | 186 (26.5) | 1.15 (0.94 to 1.40) | 1.16 (0.95 to 1.43) | |
| 3 | 445 (74.4) | 153 (25.6) | 1.20 (0.94 to 1.53) | 1.18 (0.92 to 1.52) | |
| 4+ | 736 (72.4) | 280 (27.6) | 1.08 (0.79 to 1.48) | 1.01 (0.73 to 1.39) | |
| Trend | 1.02 (0.92 to 1.13); | 1.00 (0.89 to 1.11) | |||
| p=0.69 | p=0.95 | ||||
| Income group (%)§ | 2968 | ||||
| <10s | 1547 (72.3) | 593 (27.7) | 1.00 | 1.00 | |
| 10–15s | 392 (73.1) | 144 (26.9) | 1.05 (0.78 to 1.39) | 1.12 (0.83 to 1.52) | |
| >15–20s | 101 (72.1) | 39 (27.9) | 0.99 (0.60 to 1.66) | 1.13 (0.67 to 1.89) | |
| >20s | 123 (80.4) | 30 (19.6) | 1.59 (0.96 to 2.63) | 1.79 (1.04 to 3.08) | |
| Trend per category of income | 1.10 (0.96 to 1.26); | 1.16 (1.00 to 1.34); | |||
| p=0.18 | p=0.05 | ||||
| Expenditure group (%)¶ | 2987 | ||||
| ≤4s 11.75d | 1226 (72.3) | 471 (27.8) | 1.00 | 1.00 | |
| 5s–6s 11.75d | 564 (73.2) | 207 (26.9) | 1.05 (0.78 to 1.40) | 1.29 (0.93 to 1.78) | |
| 7s–8s 11.75d | 227 (72.1) | 88 (27.9) | 0.99 (0.68 to 1.44) | 1.20 (0.82 to 1.76) | |
| >9s | 154 (75.1) | 51 (24.9) | 1.17 (0.77 to 1.78) | 1.50 (0.96 to 2.34) | |
| Trend per category of expenditure | 1.03 (0.91 to 1.17); | 1.14 (0.99 to 1.31); | |||
| p=0.61 | p=0.07 | ||||
| Social class (%)¶ | 2744 | ||||
| I/II | 128 (72.7) | 48 (27.3) | 1.00 | 1.00 | |
| III | 392 (69.1) | 175 (30.9) | 0.84 (0.47 to 1.49) | 0.71 (0.39 to 1.28) | |
| IV | 433 (71.7) | 171 (28.3) | 0.95 (0.54 to 1.65) | 1.02 (0.57 to 1.81) | |
| V | 346 (72.4) | 132 (27.6) | 0.98 (0.53 to 1.80) | 0.76 (0.41 to 1.41) | |
| Unemployed | 695 (75.6) | 224 (24.4) | 1.16 (0.66 to 2.04) | 0.82 (0.45 to 1.49) | |
| Trend per category of social class | 1.08 (0.98 to 1.19); | 1.00 (0.89 to 1.12); | |||
| p=0.13 | p=0.98 | ||||