Table 1 Socio-demographic characteristics and potential risk factors among participants (Continued) Hadjisavvas et al. BMC Cancer 2010, 10:447 http://www.biomedcentral.com/1471-2407/10/447 Table 1 Socio-demographic characteristics and potential risk factors among participants Characteristic Cases Controls (N = 1109) (N = 1177) N % N % Age <45 45-54 55-64 ≥65 Not reported Mean (SD) Education Primary Secondary Tertiary University Not reported Marital status Married Widowed/Divorced Single Not reported BMI <18.5 18.5-24.5 25-29.5 ≥30 Not reported Family history of breast cancer No Yes Not reported Age at menarche ≤11 years 12-14 years ≥15 years Pregnancy4 Yes No Number of children4 None One Two Three or more Age at 1st pregnancy5 <30 ≥30 Not reported 121 10.9 354 31.9 394 35.5 240 21.6 0 0.0 56.1 (9.1) 418 37.7 412 37.2 131 11.8 135 12.2 13 1.2 921 83.1 130 11.7 57 5.1 1 0.1 13 1.2 314 28.3 368 33.2 337 30.4 77 6.9 953 85.9 156 14.1 0 0.0 157 14.2 798 72.0 154 13.9 1021 92.1 88 7.9 103 9.3 90 8.1 480 43.3 436 39.3 851 83.4 140 13.7 30 2.9 68 5.8 440 37.4 526 44.7 140 11.9 3 0.3 55.7 (7.0) 464 39.4 435 37.0 147 12.5 122 10.4 9 0.8 1015 86.2 117 9.9 42 3.6 3 0.3 11 0.9 322 27.4 463 39.3 269 22.9 112 9.5 1068 90.7 107 9.1 2 0.2 134 11.4 838 71.2 205 17.4 1110 94.3 67 5.7 88 7.5 82 7.0 492 41.8 515 43.8 971 87.5 116 10.5 23 2.1 p- value1 <0.012 0.223 0.51 0.09 <0.001 <0.001 0.02 0.03 0.10 0.03 Breastfeeding5 Never ≤6 months 7-12 months More than 1 year Oral contraceptive use No Yes Not reported HRT use Never <6 months 6-60 months ≥60 months Not reported Smoking Never Past Current Not reported Exercise6 Yes No Not reported Page 4 of 10 305 29.9 329 32.2 166 16.3 221 21.7 823 74.2 280 25.3 6 0.5 937 84.5 41 3.7 86 7.8 45 4.1 0 0.0 869 78.4 130 11.7 108 9.7 2 0.2 544 49.1 563 50.8 2 0.2 279 25.1 385 34.7 181 16.3 265 23.9 879 74.7 294 25.0 4 0.3 838 71.2 64 5.4 182 15.5 92 7.8 1 0.1 955 81.1 76 6.5 143 12.2 3 0.3 635 54.0 539 45.8 3 0.3 0.09 0.76 <0.001 <0.001 0.06 Notes: 1P-value of c2 test for independence. 2Differences in the age distribution among cases and controls are mainly driven by the under- representation of controls in the younger and older age-groups. After restricting to ages 45-65, p-value becomes 0.46. 3P-value of t-test for difference in mean age between cases and controls. 4The difference in number of women reporting not having had a pregnancy (N = 155) and not having had a child (N = 191) is due to the fact that 15 and 21 women in cases and controls respectively have reported been pregnant not resulting in birth. 5Restricted to those women who have had a pregnancy. 6Only information on current exercise status was available. reduced across all categories of duration of breastfeeding while estimated odds ratios were of similar magnitude. The Likelihood Ratio Test comparing the goodness of fit of the model with ordered categories vs. the simpler model where breastfeeding was expressed as a binary variable produced p-values of 0.27 in the unadjusted, 0.19 and 0.33 in the adjusted models respectively, sug- gesting no evidence of an improved fit of the full model. Further adjusting for all other variables did not alter our inferences. A strong inverse association was observed between breast cancer risk and number of children. Compared to nulliparous women, crude odds ratios were 0.90, 0.84 and 0.68 in women with one, two and three chil- dren respectively; p-value for trend < 0.01. However, as expected, there was a strong association between num- ber of children and likelihood of breastfeeding. Nearly half of women with one child reported not having