Characteristics of breast cancer cases and their matched controls in the study population of Danish women
| Cases (n=38 375) (%) | Controls (n=191 875) (%) | |
| Socioeconomic status | ||
| Academics | 1870 (4.9) | 9142 (4.8) |
| Middle education | 4141 (10.8) | 18 244 (9.5) |
| Shorter education | 6709 (17.5) | 32 651 (17.1) |
| Skilled | 9165 (23.9) | 46 539 (24.2) |
| Unskilled | 7977 (20.8) | 42 324 (22.1) |
| Unknown | 8513 (22.1) | 42 875 (22.3) |
| Reproductive factors | ||
| Number of children | ||
| 0 | 4572 (11.9) | 20 865 (10.9) |
| 1–2 | 32 136 (83.8) | 160 509 (83.7) |
| ≥3 | 1667 (4.3) | 10 501 (5.4) |
| Mean number (±SD) | 1.8 (1.0) | 1.9 (1.0) |
| Age at first live birth* | ||
| <25 | 17 441 (51.6) | 93 141 (54.4) |
| 25–29 | 10 549 (31.2) | 52 367 (30.6) |
| 30–34 | 4368 (12.9) | 18 913 (11.1) |
| ≥35 | 1445 (4.3) | 6589 (3.9) |
| Mean age (±SD) | 27.2 (5.7) | 26.9 (5.7) |
| Work-related physical activity | ||
| Ever | 19 483 (50.7) | 96 184 (50.1) |
| Never | 18 892 (49.3) | 95 691 (49.9) |
| Subtypes of breast cancer | ||
| ER status | ||
| Negative | 7063 (18.5) | |
| Positive | 26 085 (67.9) | |
| Missing | 5227 (13.6) | |
*Among parous women.
ER, oestrogen receptor.