Table 1.
Descriptive characteristics of study population (n = 1121) at the time of mammography, Nurses' Health Study (1989–1998)
| Characteristic | ||
| Mean values | Mean | SD |
| Age, y | 58.4 | 7.3 |
| Body mass index, kg/m2 | 25.6 | 4.6 |
| Percentage mammographic density, % | 27.1 | 20.6 |
| Frequenciesa | N | % |
| Menopausal/hormone status | ||
| Premenopausal | 217 | 19.4 |
| Postmenopausal/never user | 371 | 33.1 |
| Postmenopausal/past user | 317 | 28.3 |
| Postmenopausal/current user | 216 | 19.3 |
| Alcohol consumption | ||
| None | 327 | 31.8 |
| <5 g/day | 346 | 33.6 |
| 5 to 14.9 g/day | 221 | 21.5 |
| 15+ g/day | 135 | 13.1 |
| Parity/age at first birth | ||
| Nulliparous | 83 | 7.5 |
| Parous/<25 years | 549 | 49.6 |
| Parous/25 to 29 years | 382 | 34.5 |
| Parous/>30 | 93 | 8.4 |
| Prior benign breast disease | 465 | 41.5 |
| Family history of breast cancer | 135 | 12.0 |
a Numbers may not be added to total due to missing data.