Table 1 Characteristics of study population in 1987 and 2006

Unweight

Weighted

Unweight

Weighted

Unweight

Weighted

 Sample size

1,398,055

94,6282,249

702,759

475,941,433

695,296

47,0340,816

 Age, mean

31.4

31.4 (31.3-31.5)

31.1

31.1 (31.0-31.2)

31.7

31.7 (31.6-31.8)

  Urban

29.4

28.8 (27.2-30.3)

29.1

28.4 (26.9-29.9)

29.8

29.1 (27.6-30.7)

  Rural

70.6

71.2 (69.7-72.8)

70.9

71.6 (70.1-73.1)

70.2

70.8 (69.3-72.4)

  Han

91.0

91.5 (90.8-92.3)

91.0

91.6 (90.8-92.3)

90.9

91.5 (90.8-92.3)

  Others

9.1

8.5 (7.7-9.2)

9.0

8.4 (7.7-9.2)

9.1

8.5 (7.7-9.2)

  Junior high school and above

31.6

31.0 (30.5-31.6)

38.0

37.6 (37.1-38.1)

25.0

24.4 (23.8-24.9)

  Primary school

39.0

39.4 (39.0-39.7)

42.7

43.2 (42.8-43.5)

35.2

35.5 (35.2-35.9)

  Never attended school

29.4

29.6 (29.1-30.0)

19.3

19.2 (18.8-19.6)

39.8

40.1 (39.5-40.7)

  Married

53.3

53.2 (53.0-53.4)

51.7

51.5 (51.3-51.7)

55.0

54.8 (54.7-55.0)

  Divorced or widowed

5.8

5.8 (5.7-5.9)

4.0

4.0 (3.9-4.1)

7.6

7.6 (7.5-7.7)

  Never married

40.9

41.0 (40.8-41.2)

44.3

44.5 (44.3-44.7)

37.4

37.5 (37.3-37.7)

  1–3

19.8

19.7 (19.4-20.1)

20.4

20.4 (20.0-20.7)

19.2

19.1 (18.7-19.5)

  4–6

61.0

61.3 (61.0-61.6)

61.3

61.6 (61.2-61.9)

60.7

61.0 (60.7-61.3)

  7–9

19.2

19.0 (18.6-19.4)

18.3

18.1 (17.6-18.5)

20.1

19.9 (19.5-20.4)

  Living with others

98.7

98.6 (78.6-79.2)

98.4

98.4 (98.3-98.4)

98.9

98.9 (98.9-99.0)

  Living alone

1.3

1.4 (1.3-1.4)

1.6

1.6 (1.5-1.7)

1.1

1.1 (1.0-1.1)

  Yes

78.8

78.9 (78.6-79.2)

86.7

86.8 (86.6-86.9)

70.8

70.9 (70.4-71.5)

  No

21.2

21.1 (20.8-21.4)

13.3

13.2 (13.1-13.4)

29.2

29.0 (28.5-29.6)

 Sample

2,526,134

1,309,468,507

1,280,006

664,280,796

1,246,128

645,187,711

 Age, mean

35.8

35.7 (35.6-35.8)

35.2

35.1 (35.0-35.2)

36.5

36.4 (36.3-36.5)

  Urban

33.9

30.8 (29.6-31.9)

32.8

30.1 (28.9-31.2)

34.3

31.4 (30.3-32.6)

  Rural

66.1

69.2 (68.1-70.4)

67.2

69.9 (68.8-71.1)

65.7

68.6 (67.4-69.7)

  Han

88.2

90.1 (89.5-90.7)

88.2

90.1 (89.4-90.7)

88.2

90.1 (89.5-90.7)

  Others

11.8

9.9 (9.3-10.5)

11.8

9.9 (9.3-10.6)

11.8

9.9 (9.3-10.5)

  Junior high school and above

49.8

48.8 (48.3-49.2)

54.9

54.1 (53.7-54.5)

44.5

43.3 (42.8-43.7)

  Primary school

31.1

31.7 (31.5-32.0)

31.3

31.9 (31.5-32.2)

30.9

31.6 (31.3-31.9)

  Never attended school

19.2

19.5 (19.3-19.7)

13.8

14.0 (12.8-14.2)

24.6

25.1 (24.8-25.5)

  Married

60.3

60.2 (60.3-60.4)

58.8

58.6 (58.4-58.8)

61.9

61.9 (61.7-62.1)

  Divorced or widowed

6.3

6.2 (6.2-6.3)

4.1

4.1 (4.1-4.2)

8.5

8.4 (8.3-8.5)

  Never married

33.4

33.6 (33.4-33.7)

37.1

37.3 (37.1-37.5)

29.7

29.7 (29.5-29.9)

  1–3

44.5

43.4 (42.9-43.9)

45.4

44.4 (43.9-44.9)

43.5

42.4 (41.9-42.9)

  4–6

50.7

51.8 (51.4-52.3)

49.9

51.0 (50.6-51.5)

51.4

52.7 (52.2-53.1)

  7–9

4.9

4.7 (4.6-4.9)

4.7

4.6 (4.4-4.7)

5.1

4.9 (4.8-5.1)

  Living with others

97.5

97.5 (97.4-97.6)

97.4

97.4 (97.4-97.5)

97.6

97.7 (97.6-97.7)

  Living alone

2.5

2.5 (2.4-2.5)

2.6

2.7 (2.5-2.6)

2.4

2.3 (2.2-2.4)

  Yes

55.3

56.1 (55.9-56.4)

59.8

60.2 (60.0-60.4)

50.8

51.9 (51.6-52.3)

  No

44.7

43.9 (43.6-44.1)

40.2

39.8 (39.6-40.0)

49.2

48.1 (47.7-48.4)

Province-level variables

Median

Median

Interquartile range

Per capita gross domestic product (yuan)

756

13313

10798-21788

Number of health professional in per 1,000 people

3.4

3.7

3.0-4.5

Proportion of agriculture, forestry, animal husbandry and fishery (%)

77

1.9

1.1-5.3

Illiterate (%)

26.2

9.2

5.2-11.3

Percentage of aged 65 and older (%)

5.5

9

8.1-10.6