Table 1.
Descriptive statistics based on percentage density
| All cases (n = 1,774) | ||||
|---|---|---|---|---|
| Unadjusted | Age-adjusted | |||
| PD <25% (n = 1,329) | PD ≥25% (n = 445) | P value | P value | |
| Age at mammography, years | 63.1 | 59.0 | <0.001 | |
| Body mass index | 26.4 | 23.9 | <0.001 | <0.001 |
| Age at menarche, years | 13.6 | 13.5 | 0.719 | 0.310 |
| Oral contraceptive use | <0.001 | 0.484 | ||
| Yes | 410 (31%) | 184 (41%) | ||
| No | 914 (69%) | 261 (59%) | ||
| Parity and age at first birth | 0.005 | 0.001 | ||
| Nulliparous | 173 (13%) | 79 (18%) | ||
| Parity ≤2 and age at first birth ≤25 | 386 (29%) | 136 (31%) | ||
| Parity ≤2 and age at first birth >25 | 403 (30%) | 144 (32%) | ||
| Parity >2 and age at first birth ≤25 | 272 (20%) | 63 (14%) | ||
| Parity >2 and age at first birth >25 | 96 (7%) | 23 (5%) | ||
| Breast feeding | 0.174 | 0.069 | ||
| Yes | 940 (80%) | 316 (77%) | ||
| No | 229 (20%) | 93 (23%) | ||
| Age at menopause, years | 50.4 | 50.5 | 0.506 | 0.046 |
| HRT use | <0.001 | <0.001 | ||
| Never | 974 (74%) | 244 (56%) | ||
| Past | 70 (5%) | 70 (16%) | ||
| Current | 268 (20%) | 124 (28%) | ||
| Previous benign breast disease | <0.001 | <0.001 | ||
| Yes | 161 (12%) | 89 (20%) | ||
| No | 1,163 (88%) | 354 (80%) | ||
| Breast cancer heredity | 0.633 | 0.829 | ||
| Yes | 200 (15%) | 64 (15%) | ||
| No | 1,091 (85%) | 376 (85%) | ||
Values other than P values are presented as number (percentage) or mean. HRT, hormone replacement therapy; PD, percentage density.