Table 2 The subgroup analysis for relative risks of childhood asthma in cesarean section

Year of publication (year)

2000–2004

8

680,637

0

0.603

1.134

1.090–1.180

< 0.001

2005–2009

11

1,937,507

73.652

< 0.001

1.256

1.115–1.415

< 0.001

2010–2014

11

581,723

0

0.823

1.191

1.145–1.239

< 0.001

2015–2018

7

1,866,897

64.631

0.009

1.234

1.089–1.397

< 0.001

Test for subgroup differences: Q = 5.189, df(Q) = 3, P = 0.158

Study design

Cohort

32

5,049,603

70.899

< 0.001

1.198

1.144–1.255

< 0.001

Case–control

3

12,373

0

0.999

1.199

1.049–1.372

0.008

Cross-sectional

2

4788

0

0.943

1.401

1.154–1.702

0.001

Test for subgroup differences: Q = 2.367, df(Q) = 2, P = 0.306

Prospective/retrospective

Prospective

15

1,716,415

49.38

0.016

1.242

1.135–1.360

< 0.001

Retrospective

22

3,350,349

70.176

< 0.001

1.195

1.132–1.261

< 0.001

Test for subgroup differences: Q = 0.523, df(Q) = 1, P = 0.470

Quality of studies

High

33

4,931,946

70.57

< 0.001

1.167

1.148–1.187

< 0.001

Moderate

4

134,818

0

0.749

1.095

0.818–1.465

0.544

Test for subgroup differences: Q = 0.427, df(Q) = 1, P = 0.514

Continent

USA

4

25,964

0

0.914

1.227

1.102–1.367

< 0.001

Europe

27

4,901,351

73.451

< 0.001

1.197

1.142–1.254

< 0.001

Asia

5

138,412

51.819

0.081

1.431

0.967–2.118

0.073

Oceania

1

1037

0

NA

0.92

0.320–2.647

0.877

Test for subgroup differences: Q = 1.182, df(Q) = 3, P = 0.757

Age of diagnosis (years)

≤ 10

20

726,194

22.466

0.177

1.182

1.135–1.231

< 0.001

> 10

4

2,097,090

80.450

0.002

1.274

1.045–1.555

0.017

Both

13

2,243,480

14.038

0.303

1.141

1.101–1.182

< 0.001

Test for subgroup differences: Q = 2.523, df(Q) = 2, P = 0.283