Table 1.

Baseline characteristics of study participants in the Breakthrough Generations Study recruited 2003–2012

Characteristic	Mean or No.	SD or %
Age at recruitment, years	46.6	13.5
Average person-time, years	6.1	1.0
Menopausal status
Postmenopausal	41,735	39.1
Premenopausal	59,627	55.9
Status not known	5216	5.0
Never had periods	34	0.0
First-degree family history of breast cancer
No	90,061	84.5
Yes	16,551	15.5
Age at first full-term pregnancy, years
≤24	25,982	24.4
25 to 34	46,690	43.8
≥35	4365	4.1
Parous, unknown age	166	0.2
Nulliparous	29,244	27.4
Parity not stated	165	0.2
Ethnicity
White	105,313	98.8
Other	1299	1.2
Socio-economic status based on place of residence
1 (highest)	48,632	45.6
2	12,200	11.4
3	30,327	28.4
4	8522	8.0
5 (lowest)	6109	5.7
No classificationa	822	0.8
Marital status
Single	13,102	12.3
Married/cohabiting	81,282	76.3
Separated/divorced	8098	7.6
Widowed	3631	3.4
Other or not known	499	0.4
Total	106,612	100.0

^a507 because they were resident in the Channel Islands, 315 for other reasons