Table 1

 Differences in sociodemographic characteristics between cases and controls

Cases(n = 133), n (%)Controls(n = 266), n (%)p Value
NA, not applicable; RMB, RenMinBi.
Age group (years)NA
    1–464 (48.1)128 (48.1)
    5–940 (30.1)80 (30.1)
    10–1429 (21.8)58 (21.8)
SexN/A
    Male80 (60.2)160 (60.2)
    Female53 (39.8)106 (39.8)
Does the child attend school / kindergarten?0.076
    Yes72 (54.1)119 (44.7)
    No61 (45.9)147 (55.3)
Did the child have severe disease (eg, high blood pressure)0.036
    Yes3 (2.3)0 (0)
    No130 (97.7)266 (100)
Father’s occupation0.847
    Farmer121 (91.0)243 (91.4)
    White-collar worker7 (5.3)14 (5.3)
    Other5 (3.8)9 (3.4)
Father’s education level0.927
    Senior high school or above12 (9.0)27 (10.2)
    Junior high school38 (28.6)77 (28.9)
    Primary school or lower83 (62.4)162 (60.9)
Mother’s education level0.496
    Senior high school or above9 (6.8)21 (7.9)
    Junior high school33 (24.8)79 (29.7)
    Primary school or lower91 (68.4)166 (62.4)
Annual household income (RMB)0.650
    ⩽300071 (53.4)129 (48.5)
    3001–500039 (29.3)85 (32.0)
    >500023 (17.3)52 (19.5)