Descriptive statistics of the study population
| Variable | Cases (%) | Controls (%) | P values |
| Age | |||
| Mean, SD | 56.82, SD=10.29 | 56.39, SD=9.90 | |
| Education | |||
| High school or less | 389 (34.5) | 300 (25.7) | |
| College/trade certificate | 339 (30.0) | 347 (29.7) | |
| University degree | 271 (24.0) | 299 (25.6) | |
| Graduate or professional school degree | 130 (11.5) | 223 (19.1) | |
| Household income (US$) | |||
| <15 000 | 70 (6.2) | 32 (2.7) | |
| 15 000–29 999 | 140 (12.4) | 89 (7.6) | |
| 30 000–59 999 | 281 (24.9) | 268 (22.9) | |
| 60 000–79 999 | 139 (12.3) | 158 (13.5) | |
| 80 000 or more | 350 (31.0) | 463 (39.6) | <0.01 |
| Not stated | 150 (13.3) | 159 (13.6) | |
| Ethnicity | |||
| European | 703 (62.2) | 912 (78.0) | |
| Chinese | 239 (21.2) | 115 (9.8) | |
| South Asian | 32 (2.8) | 34 (2.9) | |
| Filipino | 60 (5.3) | 38 (3.3) | |
| Japanese | 24 (2.1) | 14 (1.2) | |
| Other | 50 (4.4) | 42 (3.6) | |
| Mixed | 22 (1.9) | 14 (1.2) | <0.01 |
| Body mass index | |||
| Mean, SD | 25.61, SD=5.27 | 25.15, SD=5.00 | 0.05 |
| Underweight (<18.5) | 27 (2.4) | 27 (2.3) | |
| Normal (18.5–25) | 585 (52.1) | 665 (57.3) | |
| Overweight (25–30) | 336 (29.9) | 309 (26.6) | |
| Obese (30+) | 174 (15.5) | 159 (13.7) | 0.03 |
| Reproductive history | |||
| Menopausal status | |||
| Premenopausal | 434 (38.4) | 474 (40.5) | |
| Postmenopausal | 695 (61.6) | 695 (59.5) | 0.30 |
| Ever pregnant | |||
| Never | 191 (16.9) | 240 (20.5) | |
| Ever | 937 (83.1) | 928 (79.5) | 0.03 |
| Age at first pregnancy* | |||
| Years: mean, SD | 25.85, SD=5.33 | 25.42, SD=5.17 | 0.10 |
| Number of births* | |||
| Mean, SD | 2.22, SD=1.12 | 2.27, SD=0.96 | 0.34 |
| Breast feeding* | |||
| Years: mean, SD | 0.87, SD=1.06 | 1.07, SD=1.16 | <0.01 |
| Lifestyle | |||
| Oral contraceptive use | |||
| Never | 497 (44.1) | 373 (31.7) | |
| Ever | 629 (55.9) | 805 (68.3) | <0.01 |
| Age at first mammogram | |||
| Years: mean, SD | 44.69, SD=8.99 | 42.72, SD=7.70 | <0.01 |
| Family history of breast cancer | |||
| Never | 906 (80.2) | 1002 (85.7) | |
| Ever | 224 (19.8) | 167 (14.3) | <0.01 |
| Smoking | |||
| Current smoker | |||
| No | 1057 (93.7) | 1096 (93.8) | |
| Yes | 71 (6.3) | 72 (6.2) | 0.90 |
| Pack-years† | |||
| Years: mean, SD | 14.12, SD=15.46 | 12.37, SD=14.47 | 0.07 |
*Among parous women.
†Among current or previous smokers.