Table 2 Results of the Newcastle–Ottawa Scale (NOS) for assessing the quality of case–control and cohort studies in the meta-analyses

Case–control studies

Selection

Comparability

Exposure

Case

definition

Representativeness of the cases

Selection of Controls

Definition of Controls

Control for most important factor and Control for any additional factor

Ascertainment of exposure

Same method of ascertainment for cases and controls

Non-Response rate

Total score

Bravi 2018 [12]

(1)

(1)

(0)

(1)

(2)

(0)

(1)

(1)

7

Brinkman 2011 [13]

(1)

(1)

(1)

(1)

(2)

(0)

(1)

(1)

8

Shivappa 2017 [35]

(1)

(1)

(0)

(1)

(2)

(0)

(1)

(1)

7

Shivappa 2019 [36]

(1)

(1)

(0)

(1)

(2)

(0)

(1)

(1)

7

Stefani 2008 [9]

(1)

(1)

(0)

(1)

(2)

(0)

(1)

(1)

7

Cohort studies

Selection

Comparability

Outcome

Representativeness of the exposed cohort

Selection of the non-exposed cohort

Ascertainment of exposure

Outcome was not present as baseline

Control for most important factor and Control for any additional factor

Assessment of outcome

Adequate follow-up period for outcome

Adequacy of follow up of cohorts

Total score

Abufaraj 2019 [34]

(1)

(1)

(0)

(1)

(2)

(0)

(1)

(1)

7

Buckland 2014

(1)

(1)

(0)

(1)

(2)

(1)

(1)

(1)

8

Dianatinasab 2020 [10]

(1)

(1)

(1)

(1)

(1)

(1)

(1)

(1)

8

Dugu 2016 [17]

(1)

(1)

(0)

(0)

(2)

(1)

(1)

(1)

7

Schulpen 2019 [15]

(1)

(1)

(0)

(1)

(2)

(1)

(1)

(1)

8

Westhoff 2018 [11]

(1)

(1)

(0)

(0)

(2)

(0)

(1)

(1)

6

Witlox 2020 [16]

(1)

(1)

(1)

(1)

(1)

(1)

(1)

(1)

8