Table 1 Baseline characteristics of study participants in the Breakthrough Generations Study recruited 2003–2012
Characteristic | Mean or No. | SD or % |
|---|---|---|
Age at recruitment, years | 46.6 | 13.5 |
Average person-time, years | 6.1 | 1.0 |
Menopausal status | ||
 Postmenopausal | 41,735 | 39.1 |
 Premenopausal | 59,627 | 55.9 |
 Status not known | 5216 | 5.0 |
 Never had periods | 34 | 0.0 |
First-degree family history of breast cancer | ||
 No | 90,061 | 84.5 |
 Yes | 16,551 | 15.5 |
Age at first full-term pregnancy, years | ||
 ≤24 | 25,982 | 24.4 |
 25 to 34 | 46,690 | 43.8 |
 ≥35 | 4365 | 4.1 |
Parous, unknown age | 166 | 0.2 |
Nulliparous | 29,244 | 27.4 |
Parity not stated | 165 | 0.2 |
Ethnicity | ||
 White | 105,313 | 98.8 |
 Other | 1299 | 1.2 |
Socio-economic status based on place of residence | ||
 1 (highest) | 48,632 | 45.6 |
 2 | 12,200 | 11.4 |
 3 | 30,327 | 28.4 |
 4 | 8522 | 8.0 |
 5 (lowest) | 6109 | 5.7 |
 No classificationa | 822 | 0.8 |
Marital status | ||
 Single | 13,102 | 12.3 |
 Married/cohabiting | 81,282 | 76.3 |
 Separated/divorced | 8098 | 7.6 |
 Widowed | 3631 | 3.4 |
 Other or not known | 499 | 0.4 |
 Total | 106,612 | 100.0 |