Table 2 Subgroup analysis

Groups matched by age and sex [7, 8, 10, 24,25,26,27]

7

698

4891

2142

18,420

1.43

1.16–1.76

P = 0.0007

I² = 55%

Smoking status matched in both groups [8,9,10, 25]

4

203

1581

598

6138

1.52

1.05–2.19

P = 0.02

I² = 65%

Control groups made up of general population [7, 10, 25,26,27,28]

6

721

4795

2135

18,212

1.49

1.19–1.88

P = 0.0007

I² = 66%

Control group with pulmonary diseases [8, 9]

2

24

201

23

620

2.23

0.56–8.88

P = 0.25

I² = 79%

Healthy control group [24]

1

30

100

50

263

1.83

1.08–3.09

…

…

Community controls [7, 24]

2

47

152

71

447

2.50

1.24–5.06

P = 0.01

I² = 59%

Hospital controls [8,9,10, 25,26,27,28]

7

728

4944

2137

18,648

1.47

1.17–1.84

P = 0.008

I² = 61%

Diagnosis of IPF based on ATS/ERS criteria [7,8,9, 24,25,26]

6

170

857

402

3080

2.09

1.34–3.29

P = 0.001

I² = 66%

Diagnosis of DM based on FBG [7, 9, 25, 26, 28]

5

193

761

395

2872

2.38

1.43–3.97

P = 0.0009

I² = 72%

Diagnosis of DM based on subjective methods [8, 24]

2

43

204

57

323

1.62

1.02–2.58

P = 0.04

I² = 0