Table 1: Sociodemographic characteristics of respondents ().

CharacteristicValueCases (%)Controls (%)

Age 24~15 (5.38%)42 (7.53%)
30~70 (25.09%)136 (24.37%)
40~131 (46.95%)267 (47.85%)
50~63 (22.58%)113 (20.25%)

Degree of educationNo formal education1 (0.36%)0 (0.00%)
Primary school2 (0.72%)19 (3.40%)
Junior high school105 (37.63%)179 (32.08%)
Senior high or technical secondary school126 (45.16%)258 (46.24%)
Junior college or above45 (16.13%)102 (18.28%)

OccupationUnskilled; for example, trader, farming20 (7.17%)34 (6.09%)
Skilled labor; for example, driver, blue-collar worker218 (78.14%)450 (80.65%)
Professional; for example, teacher, healthcare worker, office worker6 (2.15%)20 (3.58%)
Others35 (12.54%)54 (9.68%)

Medical insuranceMedical insurance for urban workers242 (86.73%)484 (86.73%)
Rural cooperative medical service30 (10.75%)57 (10.21%)
Commercial insurance3 (1.08%)6 (1.08%)
Self-paying3 (1.08%)5 (0.90%)
Others1 (0.36%)6 (1.08%)

Average monthly incomeLess than 1000 CNY40 (14.34%)71 (12.72%)
1000–2000 CNY106 (37.99%)206 (36.92%)
2000–3000 CNY78 (27.96%)161 (28.85%)
3000–4000 CNY31 (11.11%)62 (11.11%)
4000–5000 CNY14 (5.02%)30 (5.38%)
More than 5000 CNY10 (3.58%)28 (5.02%)