Table 2 Quality assessment of case–control studies according to Newcastle–Ottawa scale.

From: Relationship between smoking and postoperative complications of cervical spine surgery: a systematic review and meta-analysis

Study

Selection

Comparability

Exposure

Total

Agrillo et al.30

****

 

**

6

Badiee et al.12

****

**

**

8

Bergin et al.32

****

**

**

8

Chen et al.33

****

**

**

8

Dube et al.34

****

**

*

7

Groff et al.37

****

*

*

6

Huang et al.16

****

**

**

8

Kang et al.38

****

**

*

7

Kimura et al.39

****

**

*

7

Klement et al.40

****

**

**

8

Lee et al.41

****

**

*

7

Lee et al.42

****

**

*

7

Liang et al.43

****

**

*

7

Liu et al.44

****

**

**

8

Nakashima et al.47

****

**

*

7

Pahys et al.14

****

**

**

8

Plano et al.49

****

*

**

7

Reinard et al.2

****

**

**

8

Ren et al.50

****

**

**

8

Riederman et al.7

****

*

**

7

Sagi et al.52

****

*

**

7

Schnee et al.29

****

 

**

6

Siemionow et al.7

****

 

**

6

Wang et al.55

****

 

**

6

Wang et al.3

****

**

**

8

Woodroffe et al.4

****

**

**

8

Zhang et al.15

****

**

**

8