Table 1

Association of family average income and conventional potential confounders

Characteristic
Family Average Income (n, %*)
p value**




Lower (N = 9689)
Middle (N = 8991)
Higher (N = 10660)


Age group(yrs)




     35–49
4127 (42.6)
4880 (54.3)
4205 (39.4)
< 0.001
     50–64
3142 (32.4)
2696 (30.0)
4115 (38.6)

     65+
2420 (25.0)
1415 (15.7)
2340 (22.0)

Gender




     Female
5063 (52.3)
4436 (49.3)
5243 (49.2)
0.581
     Male
4626 (47.7)
4555 (50.7)
5417 (50.8)

Area




     Rural
6469 (66.8)
2624 (29.2)
386 (3.6)
< 0.001
     Urban
3220 (33.2)
6367 (70.8)
10274 (96.4)

Education (yrs)




     0–9
9018 (93.1)
6872 (76.4)
3947 (37.0)
< 0.001
     10–12
641 (6.6)
1770 (19.7)
3070 (28.8)

     13+
30 (0.3)
349 (3.9)
3643 (34.2)

Occupation




     Blue collar
7585 (78.3)
5538 (61.6)
2742 (25.7)
< 0.001
     Service people
1681 (17.3)
1326 (14.7)
652 (6.1)

     White collar
423 (4.4)
2127 (23.7)
7266 (68.2)

BMI (kg/m2)




     24-
6761 (69.8)
5366 (59.7)
5967 (56.0)
< 0.001
     24–28
2362 (24.4)
2834 (31.5)
3757 (35.2)

     28+
566 (5.8)
791 (8.8)
936 (8.8)

Cigarette Smoking




     Never
6393 (66.0)
6060 (67.4)
7994 (75.0)
< 0.001
     Ex/Current
3296 (34.0)
2931 (32.6)
2666 (25.0)

Alcohol consumption




     No
7468 (77.1)
7099 (79.0)
9003 (84.5)
< 0.001
     Ex/Current
2221 (22.9)
1892 (21.0)
1657 (15.5)

Diabetes




     No
9640 (99.5)
8844 (98.4)
10227 (95.9)
< 0.001
     Yes
49 (0.5)
147 (1.6)
433 (4.1)

High blood pressure




     No
6505 (67.1)
6108 (67.9)
6987 (65.5)
0.013
     Yes
3184 (32.9)
2883 (32.1)
3673 (34.5)

Occupational physical activity




     Light
4292 (44.3)
6242 (69.4)
9761 (91.6)
< 0.001
     Moderate
1125 (11.6)
1157 (12.9)
643 (6.0)

     Vigorous
4272 (44.1)
1592 (17.7)
256 (2.4)

Leisure-time physical activity




     Light
7281 (75.1)
7502 (83.4)
8957 (84.0)
< 0.001
     Moderate
2089 (21.6)
1374 (15.3)
1643 (15.4)

     Vigorous
319 (3.3)
115 (1.3)
60 (0.6)


* Percentages across column.

**P value between sub-groups of each variable.

†Blue collar = farmer, factory worker, forestry worker, fisher and military person; Service people = salespeople, house worker and vehicle driver; White collar = office worker, teacher, doctor and academic researcher, government officer.

Xu et al. BMC Public Health 2008 8:170   doi:10.1186/1471-2458-8-170