. Author manuscript; available in PMC: 2015 May 1.

Published in final edited form as: Breast Cancer Res Treat. 2014 Mar 20;145(1):165–175. doi: 10.1007/s10549-014-2905-y

Table 2. Multivariable-adjusted Odds Ratios of Breast Cancer According to Age Group, Collaborative Breast Cancer Study, 1988-2008.

Characteristic	Women ages 18 to 39 (1,324 cases/2,038 controls)		Women ages 40 to 49 (4,315 cases/5,241 controls)		Women ages 50 to 64 (10,913 cases/13,053 controls)		Women ages 65 to 79 (7,407 cases/7,972 controls)

	Odds Ratio^a	95% CI^a	Odds Ratio^a	95% CI^a	Odds Ratio^a	95% CI^a	Odds Ratio^a	95% CI^a
Family history of breast cancer
None	1		1.00		1		1
Any	2.28	1.78, 2.92	1.92	1.70, 2.16	1.58	1.47, 1.69	1.69	1.55, 1.84
1	2.09	1.63, 2.69	1.80	1.59, 2.04	1.52	1.41, 1.63	1.58	1.44, 1.73
2	11.60	2.55, 52.82	4.44	2.73, 7.23	2.08	1.67, 2.59	2.43	1.92, 3.10
≥ 3	b	b	3.76	1.01, 14.01	2.55	1.36, 4.76	3.25	1.62, 6.51
Parity
0	1		1		1		1
1	1.10	0.81, 1.48	0.90	0.76, 1.08	0.73	0.65, 0.84	0.87	0.75, 1.01
2	0.91	0.70, 1.18	0.83	0.72, 0.96	0.73	0.65, 0.80	0.84	0.74, 0.96
≥ 3	1.14	0.19, 6.73	0.71	0.61, 0.81	0.60	0.55, 0.66	0.76	0.68, 0.86
Oral contraceptive use
Never	1		1		1		1
Ever	1.12	0.93-1.34	1.07	0.97-1.17	1.08	1.02-1.14	1.05	0.94-1.16
Body mass index (kg/m²)
< 18.5 (underweight)	0.79	0.53, 1.18	0.92	0.71, 1.21	0.73	0.59, 0.91	0.77	0.61, 0.96
18.5 - 24.9 (normal)	1		1		1		1
25 - 29.9 (overweight)	0.74	0.61, 0.90	0.89	0.81, 0.99	1.08	1.01, 1.15	1.16	1.07, 1.25
≥ 30 (obese)	0.70	0.54, 0.90	0.79	0.70, 0.89	1.16	1.09, 1.25	1.49	1.36, 1.64
Smoking status
Never	1		1		1		1
Former	1.00	0.83, 1.22	1.06	0.96, 1.17	1.06	1.00, 1.13	1.05	0.97, 1.13
Current	0.84	0.69, 1.01	0.97	0.87, 1.07	0.99	0.92, 1.06	1.12	1.01, 1.23
Recent alcohol consumption (drinks/week)
Never	1		1		1		1
< 3	1.09	0.86-1.38	1.04	0.92-1.18	0.96	0.90-1.03	1.10	1.01-1.19
3-6	1.22	0.93-1.60	1.10	0.95-1.28	1.05	0.96-1.15	1.20	1.07-1.35
7-13	1.25	0.89-1.76	1.13	0.94-1.35	1.12	1.00-1.24	1.17	1.03-1.33
14-20	0.91	0.48-1.71	1.19	0.89-1.57	1.19	1.02-1.39	1.70	1.40-2.06
21-27	2.54	1.08-5.97	1.66	0.99-2.77	1.79	1.38-2.31	2.38	1.61-3.51
28-34	1.35	0.37-4.93	1.31	0.64-2.66	1.51	1.00-2.29	2.04	1.12-3.72
≥ 35	2.17	0.77-6.09	0.94	0.53-1.68	1.97	1.33-2.93	2.32	1.30-4.12

Abbreviation: CI, confidence interval.

Odds ratios are adjusted for age, state of residence, study period, and all the other factors shown in Table 1.

Too few participants within the age stratum to estimate the odds ratio and confidence interval.

Odds ratio also adjusted for residuals of time since last use regressed on age (instead of adjusted for age).