Table 1

Characteristics of breast cancer cases and their matched controls in the study population of Danish women

Cases (n=38 375) (%)Controls (n=191 875) (%)
Socioeconomic status
 Academics1870 (4.9)9142 (4.8)
 Middle education4141 (10.8)18 244 (9.5)
 Shorter education6709 (17.5)32 651 (17.1)
 Skilled9165 (23.9)46 539 (24.2)
 Unskilled7977 (20.8)42 324 (22.1)
 Unknown8513 (22.1)42 875 (22.3)
Reproductive factors
Number of children
 04572 (11.9)20 865 (10.9)
 1–232 136 (83.8)160 509 (83.7)
 ≥31667 (4.3)10 501 (5.4)
Mean number (±SD)1.8 (1.0)1.9 (1.0)
Age at first live birth*
 <2517 441 (51.6)93 141 (54.4)
 25–2910 549 (31.2)52 367 (30.6)
 30–344368 (12.9)18 913 (11.1)
 ≥351445 (4.3)6589 (3.9)
Mean age (±SD)27.2 (5.7)26.9 (5.7)
Work-related physical activity
 Ever19 483 (50.7)96 184 (50.1)
 Never18 892 (49.3)95 691 (49.9)
Subtypes of breast cancer
ER status
 Negative7063 (18.5)
 Positive26 085 (67.9)
 Missing5227 (13.6)
  • *Among parous women.

  • ER, oestrogen receptor.