| 1930–1938 (n = 26,723) | 1939–1948 (n = 57,571) | 1949–1958 (n = 99,680) | 1959–1968 (n = 92,452) | 1969–1974 (n = 25,318) |
---|---|---|---|---|---|
Mean age/years, (SD) | 70.5 (2.4) | 61.6 (3.1) | 52.0 (3.0) | 41.8 (2.9) | 35.7 (1.4) |
Rural residency, % | 43.6 | 53.3 | 55.5 | 58.8 | 60.1 |
Urban residency, % | 56.5 | 46.7 | 44.5 | 41.2 | 40.0 |
Highest education, % | |||||
 Primary school | 85.9 | 75.0 | 63.4 | 34.7 | 38.5 |
 Middle school | 6.8 | 14.8 | 21.7 | 38.2 | 36.7 |
 High school and above | 7.3 | 10.3 | 14.8 | 27.1 | 24.7 |
Household size, % | |||||
 ≤3 people | 59.0 | 50.6 | 44.8 | 46.2 | 44.7 |
 3–5 people | 30.3 | 34.4 | 40.0 | 45.8 | 46.2 |
 >5 people | 10.7 | 15.0 | 15.2 | 8.1 | 9.1 |
BMI at age 25/(kg/m2), (SD) | 22.6 (3.2) | 22.3 (3.0) | 22.0 (2.7) | 21.5 (2.5) | 21.4 (2.5) |
Age at menarche, % | |||||
 <15 years old | 22.7 | 19.7 | 28.9 | 43.4 | 58.1 |
 ≥15 years old | 77.3 | 80.3 | 71.1 | 56.6 | 41.9 |
Age at menarche/years old, (SD) | 16.0 (2.0) | 16.3 (2.1) | 15.6 (2.0) | 14.9 (1.7) | 14.3 (1.6) |
Oral contraceptive pills use, % | |||||
 Never used | 94.7 | 90.3 | 87.6 | 90.2 | 94.6 |
Age at first birth, % | |||||
 ≤21 years old | 54.3 | 45.0 | 23.9 | 22.7 | 24.8 |
 21–25 years old | 30.4 | 38.4 | 45.5 | 59.3 | 52.8 |
 ≥25 years old | 15.3 | 16.7 | 30.6 | 18.1 | 22.4 |
Age at first birth/years old, (SD) | 22.0 (3.6) | 22.5 (3.4) | 24.0 (3.2) | 23.5 (2.7) | 23.8 (2.9) |
Numbers of live births, % | |||||
 1 | 4.4 | 5.3 | 36.1 | 55.9 | 62.9 |
 2 | 8.9 | 27.8 | 39.2 | 32.8 | 31.3 |
 >2 | 86.7 | 66.9 | 24.6 | 11.3 | 5.8 |