Table 2 The child and family characteristics in the study population (n = 114,311)

Child characteristics

Children’s age (M, SD)

4.408, 0.798

4.413, 0.797

4.403, 0.800

0.0423

4.446, 0.790

4.501, 0.781

4.490, 0.801

4.411, 0.804

4.389, 0.797

4.347, 0.782

4.472, 0.789

<0.001

Gender (n%)

<0.001

Male

59,694, 52.221

59,694, 100.000

0, 0.000

1268, 53.3

1014, 53.566

5568, 54.386

16,010, 54.868

29,670, 51.117

3373, 48.076

2791, 50.171

Female

54,617, 47.779

0, 0.000

54,617, 100.000

1111, 46.7

879, 46.434

4670, 45.614

13,169, 45.132

28,373, 48.883

3643, 51.924

2772, 49.829

BMI (M, SD)

15.602, 1.607

15.754, 1.622

15.435, 1.574

<0.001

15.660, 1.709

15.661, 1.666

15.660, 1.702

15.609, 1.617

15.576, 1.576

15.582, 1.574

15.698, 1.669

<0.001

Right-handedness (n%)

<0.001

0.007

No

8187, 7.162

4763, 7.979

3424, 6.269

212, 8.911

148, 7.818

763, 7.453

2103, 7.207

4039, 6.959

520, 7.412

402, 7.226

Yes

106,124, 92.838

54,931, 92.021

51,193, 93.731

2167, 91.089

1745, 92.182

9475, 92.547

27,076, 92.793

54,004, 93.041

6496, 92.588

5161, 92.774

Eyesight (n%)

0.506

0.147

Normal

103,199, 90.279

53,858, 90.223

49,341, 90.34

2133, 89.66

1691, 89.329

9202, 89.881

26,353, 90.315

52,463, 90.386

6302, 89.823

5055, 90.868

Abnormal

11,112, 9.721

5836, 9.777

5276, 9.66

246, 10.34

202, 10.671

1036, 10.119

2826, 9.685

5580, 9.614

714, 10.177

508, 9.132

Birth weight (n%)

<0.001

<0.001

<2500g

3700, 3.237

1727, 2.893

1973, 3.612

365, 15.343

383, 20.232

1019, 9.953

925, 3.17

808, 1.392

93, 1.326

107, 1.923

≥2500g

110,611, 96.763

57,967, 97.107

52,644, 96.388

2014, 84.657

1510, 79.768

9219, 90.047

28,254, 96.83

57,235, 98.608

6923, 98.674

5456, 98.077

Delivery mode

<0.001

<0.001

Vaginal delivery

59,625, 52.160

30,421, 50.962

29,204, 53.471

1208, 50.778

928, 49.023

5070, 49.521

13,925, 47.723

31,639, 54.51

3893, 55.487

2962, 53.245

Delivery with caesarean section

54,686, 47.840

29,273, 49.038

25,413, 46.529

1171, 49.222

965, 50.977

5168, 50.479

15,254, 52.277

26,404, 45.49

3123, 44.513

2601, 46.755

NICU admission

<0.001

<0.001

No

102,833, 89.959

53,301, 89.290

49,532, 90.69

1891, 79.487

1399, 73.904

8206, 80.152

26,290, 90.099

53,501, 92.175

6420, 91.505

5126, 92.145

Yes

11,478, 10.041

6393, 10.710

5085, 9.31

488, 20.513

494, 26.096

2032, 19.848

2889, 9.901

4542, 7.825

596, 8.495

437, 7.855

Other developmental disorders

<0.001

<0.001

No

113,565, 99.347

59,244, 99.246

54,321, 99.458

2359, 99.159

1867, 98.627

10174, 99.375

28,971, 99.287

57,702, 99.413

6977, 99.444

5515, 99.137

Yes

746, 0.653

450, 0.754

296, 0.542

20, 0.841

26, 1.373

64, 0.625

208, 0.713

341, 0.587

39, 0.556

48, 0.863

Co-sleeping

0.427

0.142

Yes

93,755, 82.020

48,941, 81.900

44,814, 82.000

1935, 81.337

1530, 80.824

8395, 81.998

23,914, 81.956

47,717, 82.21

5754, 82.013

4510, 81.071

No

20,556, 17.980

10,753, 18,100

9803, 18.000

444, 18.663

363, 19.176

1843, 18.002

5265, 18.044

10,326, 17.79

1262, 17.987

1053, 18.929

Family characteristics

Higher education of mother (n%)

0.00195

<0.001

No

51,393, 44.959

27,098, 45.395

24,295, 44.482

1086, 45.649

862, 45.536

4578, 44.716

13,540, 46.403

24,070, 41.469

2929, 41.747

2870, 51.591

Yes

62,918, 55.041

32,596, 54.605

30,322, 55.518

1293, 54.351

1031, 54.464

5660, 55.284

15,639, 53.597

33,973, 58.531

4087, 58.253

2693, 48.409

Higher education of father (n%)

0.00498

<0.001

No

52,335, 45.783

27,566, 46.179

24,769, 45.35

1061, 44.599

851, 44.955

4496, 43.915

13,709, 46.982

24,759, 42.656

2940, 41.904

2825, 50.782

Yes

61,976, 54.217

32,128, 53.821

29,848, 54.65

1318, 55.401

1042, 55.045

5742, 56.085

15,470, 53.018

33,284, 57.344

4076, 58.096

2738, 49.218

Mother’s occupation (n%)

0.00255

0.013

Employed

71,455, 62.509

37,561, 62.923

33,894, 62.058

1505, 63.262

1165, 61.543

6231, 60.861

18,247, 62.535

36,361, 62.645

4439, 63.27

3507, 63.042

Unemployed

42,856, 37.491

22,133, 37.077

20,723, 37.942

874, 36.738

728, 38.457

4007, 39.139

10,932, 37.465

21,682, 37.355

2577, 36.73

2056, 36.958

Father’s occupation (n%)

0.249

<0.001

Employed

90,554, 79.217

47,367, 79.35

43,187, 79.072

1834, 77.091

1452, 76.704

7755, 75.747

23,101, 79.17

46,381, 79.908

5655, 80.601

4376, 78.663

Unemployed

23,757, 20.783

12,327, 20.65

11,430, 20.928

545, 22.909

441, 23.296

2483, 24.253

6078, 20.83

11,662, 20.092

1361, 19.399

1187, 21.337

Family annual per capita income (RMB) b(n%)

0.0326

<0.001

Below

21,988, 19.235

11,340, 18.997

10,648, 19.496

526, 22.11

431, 22.768

2371, 23.159

5418, 18.568

10,683, 18.405

1296, 18.472

1263, 22.704

Above or equal to

92,323, 80.765

48,354, 81.003

43,969, 80.504

1853, 77.89

1462, 77.232

7867, 76.841

23,761, 81.432

47,360, 81.595

5720, 81.528

4300, 77.296

Family structure (n%)

0.0395

<0.001

Single families

2807, 2.456

1412, 2.365

1395, 2.554

89, 3.741

59, 3.117

340, 3.321

748, 2.563

1242, 2.140

155, 2.209

174, 3.128

Nuclear families

70,142, 61.361

36,724, 61.520

33,418, 61.186

1544, 64.901

1225, 64.712

6581, 64.28

17,989, 61.651

35,235, 60.705

4058, 57.839

3510, 63.095

Extended families

41,362, 36.184

21,558, 36.114

19,804, 36.260

746, 31.358

609, 32.171

3317, 32.399

10,442, 35.786

21,566, 37.155

2803, 39.952

1879, 33.777

The number of children in the family (n%)

<0.001

<0.001

One

64,273, 56.226

34,319, 57.492

29,954, 54.844

1390, 58.428

1125, 59.429

5616, 54.854

15,516, 53.175

33,105, 57.035

4201, 59.877

3320, 59.680

Two or more

50,038, 43.774

25,375, 42.508

24,663, 45.156

989, 41.572

768, 40.571

4622, 45.146

13,663, 46.825

24,938, 42.965

2815, 40.123

2243, 40.320

Maternal health characteristics

Maternal age at delivery (n%)

0.414

<0.001

<30

84,676, 74.075

44,158, 73.974

40,518, 74.186

1766, 74.233

1354, 71.527

7068, 69.037

20,500, 70.256

44,021, 75.842

5686, 81.043

4281, 76.955

30–34

21,956, 19.207

11,582, 19.402

10,374, 18.994

417, 17.528

367, 19.387

2224, 21.723

6293, 21.567

10,666, 18.376

1049, 14.952

940, 16.897

≥35

7679, 6.718

3954, 6.624

3725, 6.820

196, 8.239

172, 9.086

946, 9.24

2386, 8.177

3356, 5.782

281, 4.005

342, 6.148

Smoking or passive smoking during pregnancy (n%)

0.685

<0.001

No

82,461, 72.137

43,031, 72.086

39,430, 72.194

1677, 70.492

1336, 70.576

7154, 69.877

21,197, 72.645

42,124, 72.574

5019, 71.536

3954, 71.077

Yes

31,850, 27.863

16,663, 27.914

15,187, 27.806

702, 29.508

557, 29.424

3084, 30.123

7982, 27.355

15,919, 27.426

1997, 28.464

1609, 28.923

Maternal complications during pregnancy c(n%)

0.147

<0.001

No

108,934, 95.296

56,938, 95.383

51,996, 95.201

2242, 94.241

1755, 92.71

9612, 93.886

27,515, 94.297

55,634, 95.85

6783, 96.679

5393, 96.944

Yes

5377, 4.704

2756, 4.617

2621, 4.799

137, 5.759

138, 7.29

626, 6.114

1664, 5.703

2409, 4.15

233, 3.321

170, 3.056