Table 1.
Baseline characteristics of the participants, by case-control status
| Controls (n = 684) | Cases (n = 414) | |
|---|---|---|
| Age, years, at mammography | ||
| Mean (SD) | 59.5 (6.6) | 67.5 (12.7) |
| Missing, n | 6 | 2 |
| Ethnicity | ||
| White, n (%) | 519 (76.4) | 370 (90.5) |
| Other, n (%) | 160 (23.6) | 39 (9.5) |
| Missing, n | 5 | 5 |
| Body mass index at mammographya, kg/m2 | ||
| Mean (SD) | 26.1 (5.6) | 26.4 (4.9) |
| Missing, n | 29 | 46 |
| Menopausal status at mammographyb | ||
| Premenopausal and perimenopausal, n (%) | 91 (13.4) | 55 (13.3) |
| Postmenopausal, n (%) | 590 (86.6) | 358 (86.7) |
| Missing, n | 3 | 1 |
| Ever use of oral contraceptives | ||
| Yes, n (%) | 208 (31.2) | 143 (36.8) |
| No, n (%) | 458 (68.8) | 246 (63.2) |
| Missing, n | 18 | 25 |
| Ever use of hormonal therapy | ||
| Yes, n (%) | 197 (29.4) | 175 (44.8) |
| No, n (%) | 472 (70.6) | 216 (55.2) |
| Missing, n | 15 | 23 |
| Parity | ||
| Yes, n (%) | 466 (69.0) | 343 (84.0) |
| No, n (%) | 209 (31.0) | 65 (15.9) |
| Missing, n | 9 | 6 |
| Number of childrenc | ||
| 1 to 2, n (%) | 300 (65.4) | 218 (47.2) |
| 3 to 4, n (%) | 126 (27.5) | 231 (50.0) |
| 5+, n (%) | 33 (7.2) | 13 (2.8) |
| Missing, n | 7 | 7 |
aBody mass index estimated form self-reported height and weight as weight/height2 (in kg/m2). bPostmenopausal women defined as those who self-reported natural (i.e. cessation of menses for at least 12 months) or surgical menopause, were ≥55 years of age, or had ever used hormone therapy. Due to small numbers premenopausal (i.e. <55 years and still having regular periods) and perimenopausal (i.e. <55 years and having irregular periods) women were combined into a single category. cRestricted to ever-parous women