Table 1 Characteristics* of participants admitted to hospital for hip or knee replacement for osteoarthritis and of all women included in the analyses
Hip replacementKnee replacementAll women
No. of women12 12499771 306 081
Mean age, years (SD)58.6 (4.5)58.9 (4.5)56.0 (4.7)
Mean BMI (SD)27.6 (5.0)30.1 (5.3)26.2 (4.7)
Percentage in upper third socioeconomic group (n)31.0 (3726)27.2 (2690)33.3 (432 291)
Percentage current smokers (n)18.9 (2143)14.2 (1303)18.9 (254 001)
Mean alcohol intake, units/week (SD)3.9 (5.1)3.1 (4.4)4.3 (5.2)
Percentage current user of HRT (n)†33.2 (2051)33.5 (1760)33.0 (333 573)
Percentage ever used oral contraceptives (n)51.1 (6118)48.7 (4774)59.8 (772 033)
Percentage with hysterectomy (n)24.0 (2719)32.9 (2984)23.0 (284 349)
Mean age at menarche, years (SD)13.0 (1.6)12.9 (1.7)13.0 (1.6)
Mean age at menopause, years (SD)‡49.5 (4.6)49.2 (5.1)49.5 (4.5)
Mean parity (SD)2.3 (1.3)2.4 (1.4)2.1 (1.2)
  • *Characteristics based on categories reported at recruitment except HRT, which is based on last reported use of HRT (see Methods). Percentages exclude those with missing values. †In 1 010 914 postmenopausal women. ‡In 350 586 postmenopausal women (with a natural menopause) who never used HRT and were aged over 52 years at recruitment.

  • BMI, body mass index; HRT, hormone replacement therapy.