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Table 1 Baseline characteristics of cohort participants

From: Timing of pubertal stages and breast cancer risk: the Breakthrough Generations Study

Variable Mean [SD] or N (%)
Age at recruitment, years 46.7 [13.4]
Average person-time, years 4.1 [1.7]
Adult height, cm 164.3 [6.6]
Menopausal status  
Postmenopausal 44,373 (42.3)
Premenopausal 60,534 (57.7)
Never periods 24 (0.0)
Family history of breast cancer  
No 89,069 (84.9)
Yes 15,862 (15.1)
Age at first full-term pregnancy, years  
≤24 25,700 (24.5)
25 to 29 31,104 (29.6)
≥30 19,285 (18.4)
Parous; age not reported 166 (0.2)
Nulliparous 28,513 (27.2)
Parity missing 163 (0.2)
Ethnicity  
White 103,655 (98.8)
Mixed white/non-white 585 (0.5)
Non-white 611 (0.6)
Missing 80 (0.1)
Socio-economic statusa  
1 (Highest) 47,952 (45.7)
2 12,001 (11.4)
3 29,886 (28.5)
4 8,449 (8.0)
5 (Lowest) 6,042 (5.8)
Channel islands/isle of manb 497 (0.5)
Unclassified 104 (0.1)
Total 104,931 (100.0)
  1. SD, Standard deviation.
  2. aSocio-economic status was based on placed of residence (Acorn scores).
  3. bResidence-based socio-economic status not classifiable.