Table 1 Demographics of the children who participated in the study

Gender(n,(%))

 Boys

16142(62.3)

3667(62.8)

3200(62.8)

2810(63.6)

2306(63.0)

2316(61.5)

1843(58.8)

21.864

<0.001

 Girls

9778(37.7)

2176(37.2)

1899(37.2)

1611(36.4)

1353(37.0)

1449(38.5)

1290(41.2)

Age (years)(M(Q₁,Q₃))(n,(%))

2.58 (1.00,6.25)

2.25 (0.88,5.67)

2.75 (1.08,6.58)

3.08 (1.17,6.92)

2.42 (1.00,5.83)

2.42 (1.08,6.17)

2.83 (1.08,5.92)

180.997

<0.001

 A[0~1)

5745(22.2)

1634(28.0)

1049(20.6)

837(18.9)

902(24.7)

710(18.9)

613(19.6)

296.243

<0.001

 B[1~3)

8049(31.1)

1690(28.9)

1582(31.0)

1279(28.9)

1131(30.9)

1371(36.4)

996(31.8)

 C[3~7)

6811(26.3)

1470(25.2)

1320(25.9)

1230(27.8)

957(26.2)

931(24.7)

903(28.8)

 D[7~13)

4998(19.3)

982(16.8)

1070(21.0)

1015(23.0)

630(17.2)

709(18.8)

592(18.9)

 E[13~18]

317(1.2)

67(1.1)

78(1.5)

60(1.4)

39(1.1)

44(1.2)

29(0.9)

Ethnicity(n,(%))

 Han nationality

24504(94.5)

5450(93.3)

4723(92.6)

4200(95.0)

3514(96.0)

3603(95.7)

3014(96.2)

98.516

<0.001

 Other Minorities

1416(5.5)

393(6.7)

376(7.4)

221(5.0)

145(4.0)

162(4.3)

119(3.8)

Region of residence(n,(%))

 Urban area

17413(67.2)

3880(66.4)

3426(67.2)

2948(66.7)

2480(67.8)

2564(68.1)

2115(67.5)

4.287

0.509

 Rural area

8507(32.8)

1963(33.6)

1673(32.8)

1473(33.3)

1179(32.2)

1201(31.9)

1018(32.5)

Where the child plays(n,(%))

 At home

11221(43.3)

1922(32.9)

1637(32.1)

1473(33.3)

2115(57.8)

2229(59.2)

1845(58.9)

708.972

<0.001

 Outdoors

14699(56.7)

3921(67.1)

3462(67.9)

2948(66.7)

1544(42.2)

1536(40.8)

1288(41.1)

Fuel for heating(n,(%))

 Oil, coal, pellet or other wood

7040(27.2)

1525(26.1)

1315(25.8)

1176(26.6)

1006(27.5)

1088(28.9)

930(29.7)

24.905

<0.001

 Other fuels

18880(72.8)

4318(73.9)

3784(74.2)

3245(73.4)

2653(72.5)

2677(71.1)

2203(70.3)

Staying in rooms at home where people smoke(n,(%))

 Never

10309(39.8)

2583(44.2)

2136(41.9)

1880(42.5)

1464(40.0)

1300(34.5)

946(30.2)

59.792

<0.001

 Not daily

7975(30.8)

1794(30.7)

1606(31.5)

1347(30.5)

1145(31.3)

1143(30.4)

940(30.0)

 Daily

7636(29.4)

1466(25.1)

1357(26.6)

1194(27.0)

1050(28.7)

1322(35.1)

1247(39.8)

Non-alcoholic beverage intake(n,(%))

 Never

6475(25.0)

1730(29.6)

1453(28.5)

1053(23.8)

838(22.9)

790(21.0)

611(19.5)

32.051

<0.001

 Not daily

16083(62.0)

3523(60.3)

2998(58.8)

2785(63.0)

2331(63.7)

2410(64.0)

2036(65.0)

 Daily

3362(13.0)

590(10.1)

648(12.7)

583(13.2)

490(13.4)

565(15.0)

486(15.5)

Annual household income(n,(%))

 ≤ 60K

8220(31.7)

1753(30.0)

1448(28.4)

1233(27.9)

1288(35.2)

1370(36.4)

1128(36.0)

48.808

<0.001

 > 60K

17700(68.3)

4090(70.0)

3651(71.6)

3188(72.1)

2371(64.8)

2395(63.6)

2005(64.0)