Table 1.
Study population characteristics, by digital mammography machine manufacturer.
| Characteristic | Hologic Study | GE Study | ||
|---|---|---|---|---|
| N=19699 | N=3757 | |||
| n | % | n | % | |
| Age (years), mean ± SD | 61.9 | ± 8.6 | 59.3 | ± 8.9 |
| Age at Menarche (years) | ||||
| <11 | 4200 | 21.3 | 777 | 20.7 |
| 12–13 | 10729 | 54.5 | 2079 | 55.3 |
| 14–15 | 3417 | 17.4 | 635 | 16.9 |
| 16+ | 722 | 3.7 | 166 | 4.4 |
| Missing | 631 | 3.2 | 100 | 2.7 |
| BMI (kg/m2), mean ± SD | 27.7 | ± 6.2 | 26.9 | ± 5.8 |
| Late adolescent BMI (kg/m2), mean ± SD | ||||
| 1st quartile | 18.1 | ± 0.9 | 18.1 | ± 0.9 |
| 2nd quartile | 20.0 | ± 0.4 | 19.9 | ± 0.4 |
| 3rd quartile | 21.4 | ± 0.4 | 21.4 | ± 0.5 |
| 4th quartile | 25.0 | ± 3.1 | 24.9 | ± 3.4 |
| Missing, n | 1883 | 361 | ||
| Age at first birth (years) | ||||
| <20 | 2111 | 10.7 | 360 | 9.6 |
| 20–24 | 5516 | 28.0 | 990 | 26.4 |
| 25–29 | 4553 | 23.1 | 785 | 20.9 |
| 30–34 | 2267 | 11.5 | 411 | 10.9 |
| 35–40 | 926 | 4.7 | 177 | 4.7 |
| >40 | 209 | 1.1 | 36 | 1.0 |
| Missing | 2302 | 11.7 | 558 | 14.8 |
| Number of births | ||||
| None | 1815 | 9.2 | 440 | 11.7 |
| 1 | 3006 | 15.3 | 545 | 14.5 |
| 2 | 7633 | 38.8 | 1314 | 35.0 |
| 3 | 3409 | 17.3 | 608 | 16.2 |
| 4+ | 1648 | 8.4 | 309 | 8.2 |
| Missing | 2188 | 11.1 | 541 | 14.4 |
| MHT use within 5 years prior to mammogram | ||||
| Yes | 4662 | 23.7 | 1140 | 30.3 |
| No | 15037 | 76.3 | 2617 | 69.7 |
| Menopausal status | ||||
| Premenopause | 4676 | 23.7 | 1031 | 27.4 |
| Postmenopause | 15023 | 76.3 | 2726 | 72.6 |
| First-degree relative with breast cancer | ||||
| Yes | 1865 | 9.5 | 358 | 9.5 |
| No | 17834 | 90.5 | 3399 | 90.5 |
| Breast cancer diagnosis prior to mammogram | ||||
| Yes | 1127 | 5.7 | 199 | 5.3 |
| No | 18572 | 94.3 | 3558 | 94.7 |
| Physical activity (METs), mean ± SD | ||||
| 1st quartile | 61.7 | ± 69.4 | 64.7 | ± 70.0 |
| 2nd quartile | 411.8 | ± 122.1 | 413.6 | ± 120.0 |
| 3rd quartile | 953.1 | ± 204.0 | 950.5 | ± 196.8 |
| 4th quartile | 2243.9 | ± 749.9 | 2187.4 | ± 693.8 |
| Missing, n | 396 | 72 | ||
| Alcohol use (drinks per week) | ||||
| None | 7926 | 40.2 | 1487 | 39.6 |
| 1–4 | 6122 | 31.1 | 1116 | 29.7 |
| 5+ | 5651 | 28.7 | 1154 | 30.7 |
| Tobacco use (packs per day) | ||||
| Never | 11969 | 60.8 | 2264 | 60.3 |
| <1/2 | 2507 | 12.7 | 436 | 11.6 |
| 1/2–1 | 2980 | 15.1 | 607 | 16.2 |
| 1+ | 2243 | 11.4 | 450 | 12.0 |
| MD phenotypes, mean ± SD | ||||
| Percent density (%) | 20.4 | ± 14.9 | 24.4 | ± 17.1 |
| Dense area (cm2) | 27.9 | ± 17.9 | 29.0 | ± 20.9 |
| Nondense area (cm2) | 140.0 | ± 77.7 | 109.2 | ± 61.0 |
| MD phenotypes (square-root), mean ± SD | ||||
| Percent density | 4.2 | ± 1.6 | 4.6 | ± 1.8 |
| Dense area | 5.0 | ± 1.6 | 5.0 | ± 1.9 |
| Nondense area | 11.3 | ± 3.3 | 10.0 | ± 2.9 |
MD = Mammographic density; GE = General Electric; BMI = body mass index; MHT = menopausal hormone therapy; MET = metabolic equivalent; SD = standard deviation.