Table 1.

Incidence of breast cancer by characteristics of the participants of the SBSP

Characteristics	No. of subjects	No. of cases	Person years	Incidence (/100,000 PYs)	HR (95% CI)
All subjects	14464	66	34001	194	—
Age (yrs.)
< 40	1020	0	2122	0	—
40-	2833	9	6848	131	0.60 (0.28, 1.27)
50-	5349	29	13200	220	1.00 (ref.)
60-	4213	23	9712	237	1.07 (0.62, 1.85)
70-	1049	5	2118	236	1.05 (0.40, 2.72)
Education
Primary school or No formal education	3324	17	8940	190	1.23 (0.62, 2.44)
Junior middle school	5646	18	13361	135	1.00 (ref.)
Senior high school or technical school	3739	21	8099	259	1.86 (0.99, 3.49)
Junior college	1018	6	2148	279	2.44 (0.96, 6.19)
Regular college or above	737	4	1454	275	2.91 (0.97, 8.72)
Family history of breast cancer
Yes	366	5	858	583	3.03 (1.22, 7.54)
No	14098	61	33143	184	1.00 (ref.)
Age at menarche (yrs.)
≤ 13	2078	15	4582	327	1.99 (1.10, 3.58)
14-17	10330	44	24273	181	1.00 (ref.)
> 17	2053	7	5142	136	0.66 (0.29, 1.47)
Menopausal status
Pre-menopause	4455	12	10510	114	0.81 (0.32, 2.04)
Post-menopause	9996	54	23462	230	1.00 (ref.)
Age at menopause (yrs.)
< 45	721	4	1704	235	1.12 (0.41, 3.11)
45-54	8323	44	19523	225	1.00 (ref.)
≥ 55	952	6	2234	269	1.20 (0.51, 2.81)
Age at first live birth (yrs.)
Nulliparity	299	0	643	0	—
< 24	3290	13	7940	164	0.99 (0.51, 1.92)
24-29	9121	39	21691	180	1.00 (ref.)
≥ 30	1750	14	3718	377	2.01 (1.09, 3.71)

Missing values were excluded from the analysis (3 subjects for age at menarche, 13 for menopause status and 4 for age at first live birth).