. 2013 May 1;24(7):1347–1356. doi: 10.1007/s10552-013-0213-1

Table 1.

Selected characteristics of the study population, stratified by birth cohort and smoking status, among 302,865 Norwegian women (1974–2003)

Birth cohort (year of birth)	<1946		1946–1950		1951–1955		>1955		Total
Characteristics/smoking status	Ever	Never	Ever	Never	Ever	Never	Ever	Never	Total
Subjects	34,950	35,088	49,165	30,067	57,766	32,997	37,481	25,351	302,865
Age^a, (mean), SD	50 ± 12	54 ± 14	42 ± 3	42 ± 3	42 ± 3	42 ± 3	39 ± 5	38 ± 6	44 ± 9
Person years of follow-up	657,363	654,555	781,699	480,232	665,721	381,025	325,583	218,137	4,164,314
Number of primary invasive breast cancers	1,226	1,136	1,620	927	1,232	713	384	252	7,490
Follow-up years, (median)	19	19	16	16	12	12	9	9	14
≥13 years of education (%)	10	14	14	29	18	38	16	35	21
Age at diagnosis, (mean), SD	61 ± 9	63 ± 11	52 ± 5	52 ± 5	49 ± 4	49 ± 5	46 ± 4	46 ± 4	54 ± 9
Nulliparous women	4,456	5,112	4,496	3,210	6,272	3,738	4,929	4,310	36,523
Parous women	30,494	29,976	44,669	26,857	51,494	29,259	32,552	21,041	266,342
Number of children, (mean), SD	2 ± 2	2 ± 2	2 ± 1	2 ± 1	2 ± 1	2 ± 1	2 ± 1	2 ± 1	2 ± 1
Age at first childbirth, (mean), SD	24 ± 4	25 ± 5	23 ± 4	24 ± 4	23 ± 5	25 ± 5	24 ± 5	26 ± 5	24 ± 5
Age at smoking initiation^b (year), SD	24 ± 8	NA	21 ± 5	NA	19 ± 5	NA	17 ± 3	NA	20 ± 6
Age at smoking initiation among nulliparous^b (year), SD	24 ± 7	NA	21 ± 5	NA	19 ± 4	NA	18 ± 4	NA	20 ± 6
Women smoking before first childbirth^b (%)	62	NA	63	NA	81	NA	94	NA	76
Body mass index^a (kg/m²)	25	26	24	24	24	25	25	25	25
Level of physical activity, heavy^a,c (%)	11	12	10	12	31	33	27	32	21
Smoking status^a (%)	50	50	62	38	64	36	60	40	59

Ever smoker: current or former daily smokers

SD standard deviation, NA not applicable

^aAt enrollment, ^bInformation not available for all smokers, ^cLight sports or heavy gardening ≥4 h per week, heavy exercise or daily competitive sports