Table 2 The quality of included studies, assessed by Newcastle–Ottawa Scale

Author, year

Study type

Comparability

Overall

Representative exposed cohort

Selection of the non-exposed cohort

Ascertainment of exposure

Outcome not present at start

Comparability based on design or analysis

Assessment of outcome

Follow-up long enough for outcomes to occur

Adequacy of follow-up of cohorts

Peng 2019 [14]

Cohort study

*

*

*

*

**

*

*

*

8

Guo 2019 [15]

Cohort study

*

*

*

*

**

*

*

*

9

Cunningham 2019 [17]

Cohort study

*

*

*

**

*

*

7

Xin 2017 [19]

Cohort study

*

*

*

*

**

*

*

8

Culley 2017 [22]

Cohort study

*

*

*

**

*

*

*

8

Yen 2016 [24]

Cohort study

*

*

*

*

**

*

*

*

9

Guo 2016 [25]

Cohort study

*

*

*

**

*

*

*

8

Cerejeira 2013 [27]

Cohort study

*

*

*

*

**

*

*

8

Flink 2012 [28]

Cohort study

*

*

*

*

**

*

*

*

9

Jankowski 2011 [29]

Cohort study

*

*

*

*

**

*

*

*

9

Priner 2008 [30]

Cohort study

*

*

*

**

*

*

7

Lowery 2008 [31]

Cohort study

*

*

*

*

*

*

*

7

Freter 2005 [33]

Cohort study

*

*

*

*

*

5

Fisher 1995 [34]

Cohort study

*

*

*

*

*

*

6

Rogers 1989 [35]

Cohort study

*

*

*

*

*

5

Author year

Study type

Comparability

Overall

Adequate case definition

Representativeness of the cases

Selection of the controls

Definition of the controls

Comparability based on design or analysis

Ascertainment of exposure (blinding)

Same method of ascertainment for subjects

Non-response rate

de Jong 2019 [16]

Case-control study

*

*

*

*

*

*

6

Tak kyu 2018 [18]

Case-control study

*

*

*

*

*

*

*

*

8

Wang 2017 [20]

Case-control study

*

*

*

*

*

*

6

Huang 2017 [21]

Case-control study

*

*

*

*

*

*

6

Choi 2017 [23]

Case-control study

*

*

*

*

*

*

*

*

8

Chung 2015 [26]

Case-control study

*

*

*

*

*

*

*

7

Wacker 2006 [32]

Case-control study

*

*

*

*

**

*

7