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. Author manuscript; available in PMC: 2015 Oct 2.
Published in final edited form as: Int J Cancer. 2013 Dec 18;135(1):186–195. doi: 10.1002/ijc.28644

Table 1. Demographic and selected breast cancer risk factors among parous participants; the Shanghai Breast Cancer Study.

Characteristic Cases (n=3443) Controls (n=3474) P
n / mean 1 % / sd 2 n / mean 1 % / sd 2
Study Phase
 I 1381 42.25 1495 44.75
 II 1888 57.75 1846 55.25 0.040
Age (years) 3 49.89 8.13 50.28 8.68 0.059
Education
 Elementary School or less 280 8.57 420 12.57
 Junior High School 1300 39.77 1389 41.57
 Senior High School 1224 37.44 1174 35.14
 College or more 465 14.22 358 10.72 <.001
Age at Menarche 14.42 1.63 14.68 1.74 <.001
Menopausal Status
 Premenopausal 1970 60.26 1890 56.59
 Postmenopausal 1299 39.74 1450 43.41 0.002
Age at Menopause a 49.91 3.40 49.33 3.75 <.001
Number of Pregnancies
 1 693 21.20 648 19.40
 2 1154 35.30 1131 33.85
 3 775 23.71 839 25.11
 ≥4 647 19.79 723 21.64 0.052
Number of Live Births
 1 2376 72.68 2285 68.39
 2 629 19.24 698 20.89
 3 184 5.63 239 7.15
 ≥4 80 2.45 119 3.56 <.001
Abortion
 Never 1168 35.73 1156 34.60
 Ever 2101 64.27 2185 65.40 0.336
Breastfeeding
 Never 750 22.94 689 20.62
 Ever 2519 77.06 2652 79.38 0.022
Lifetime Duration of Breastfeeding (months) b 13.2 11.48 14.85 12.97 <.001
Breast Cancer among First Degree Relatives
 Never 3118 95.38 3249 97.25
 Ever 151 4.62 92 2.75 <.001
Ever had Breast Fibroadenoma
 Never 2942 90.25 3158 94.58
 Ever 318 9.75 181 5.42 <.001
Oral Contraceptive Use
 Never 2612 79.90 2647 79.23
 Ever 657 20.10 694 20.77 0.497
Hormone Replacement Therapy
 Never 3140 96.11 3243 97.07
 Ever 127 3.89 98 2.93 0.033
Body Mass Index (BMI) 23.69 3.30 23.35 3.29 <.001
Ever Smoking
 Never 3180 97.28 3245 97.13
 Ever 89 2.72 96 2.87 0.710
Ever Drinking
 Never 3120 95.47 3152 94.43
 Ever 148 4.53 186 5.57 0.053
Physical Activities in recent 10 years
 Never 2467 75.47 2330 69.74
 Ever 802 24.53 1011 30.26 <.001
1

n for categorical variables or mean for continuous variables

2

% for categorical variables or standard deviation(sd) for continuous variables

3

Age at diagnosis for cases or age at interview for controls

a

Among women with natural menopause

b

Among women who ever breastfed