Table 1.
Selected baseline characteristics of the study population
| Variable§ | Cases (N=497) | Subcohort (N=2,830) | P-value¶ |
|---|---|---|---|
| Age (years) | 65 (59 to 70) | 63 (57 to 69) | <.0001 |
| Women’s Health Initiative, N(%) | |||
| Observational Study Cohort | 401 (80.7) | 756 (26.7) | N/A |
| Clinical Trial Cohort | 96 (19.3) | 2074 (73.3) | |
| Ethnicity, N (%) | |||
| White | 394 (79.3) | 1591 (56.4) | <.0001 |
| Black | 60 (12.1) | 634 (22.4) | |
| Hispanic | 22 (4.4) | 340 (12.0) | |
| Asian/other | 19 (3.8) | 263 (9.2) | |
| Missing | 2 (0.4) | 2 (0.1) | |
| Body mass index (BMI; Kg/M2), N(%) | 0.17 | ||
| Normal (BMI<25.0) | 155 (31.2) | 762 (26.9) | |
| Overweight (25.0-<30.0) | 165 (33.2) | 998 (35.3) | |
| Obese (≥30.0) | 177 (35.6) | 1070 (37.8) | |
| Age at Menarche, N (%) | 0.44 | ||
| ≤10 | 41 (8.2) | 193 (6.8) | |
| 11-12 | 203 (40.8) | 1101 (38.9) | |
| 13+ | 250 (50.3) | 1523 (53.8) | |
| Missing | 3 (0.7) | 13 (0.5) | |
| Age at Menopause, N(%) | 0.001 | ||
| ≤42 | 72 (14.5) | 541 (19.1) | |
| 43-48 | 106 (21.3) | 629 (22.2) | |
| 49-51 | 133 (26.8) | 616 (21.8) | |
| ≥52 | 142 (28.6) | 675 (23.9) | |
| Missing | 44 (8.8) | 369 (13.0) | |
| Parity, N(%) | 0.04 | ||
| 0 | 79 (15.9) | 334 (11.8) | |
| 1 | 39 (7.8) | 254 (9.0) | |
| ≥2 | 375 (75.5) | 2223 (78.6) | |
| Missing | 4 (0.8) | 19 (0.6) | |
| Family history of breast cancer, (N%), | <.0001 | ||
| Yes | 138 (27.8) | 440 (15.5) | |
| No | 185 (37.2) | 2164 (76.5) | |
| Missing | 174 (35.0) | 226 (8.0) | |
| Smoking status, N (%) | 0.001 | ||
| Never | 254 (51.1) | 1519 (53.7) | |
| Former | 213 (42,9) | 1021 (36.1) | |
| Current | 22 (4.4) | 250 (8.8) | |
| Missing | 8 (1.6) | 40 (1.4) | |
| Education history, N (%) | <.0001 | ||
| High school and less | 144 (29.0) | 1125 (39.8) | |
| College | 203 (40.8) | 982 (34.7) | |
| Postgraduate education | 143 (28.8) | 701 (24.8) | |
| Missing | 7 (1.4) | 22 (0.7) | |
| Alcohol (servings per week) | 0.4 (0.0 to 3.5) | 0.2 (0.0 to 1.4) | <.0001 |
| Physical activity (METs‡) | 8.29 (2.00 to 17.50) | 5.75 (0.50 to 15.00) | <.0001 |
P-values derived from Wilcoxon rank sum test for continuous data and Pearson’s chi-square for categorical data.
‡
MET, metabolic equivalent tasks (defined as the caloric need per kilogram of body weight per hour of activity divided by the caloric need per kilogram of body weight per hour at rest) per hour per week.
§
Values are medians (inter-quartile range) unless otherwise stated.