Table 2 Newcastle-Ottawa scale for assessing the quality of included studies

Study design

Author, year

Selection (Max = 4)

Comparability (Max = 2)

Outcome (Max = 3)

Overall quality score (Max = 9)

Cross-sectional study

Magee et al. 2018 [8]

3

2

3

8

Study design

Author, year

Selection (Max = 4)

Comparability (Max = 2)

Exposure (Max = 3)

Overall quality score (Max = 9)

Case-control study

Marupuru et al. 2017 [19]

4

1

2

7

Study design

Author, year

Selection (Max = 4)

Comparability (Max = 2)

Outcome (Max = 3)

Overall quality score (Max = 9)

Cohort study

Tseng 2018 [7]

4

2

2

8

Pan et al. 2018 [13]

4

2

2

8

Ma et al. 2018 [21]

4

1

3

8

Lin et al. 2018 [10]

4

2

2

8

Lee et al. 2018 [9]

4

2

2

8

Degner et al. 2018 [12]

4

2

2

8

Lin et al. 2017 [20]

4

2

2

8

Lee et al. 2017 [11]

4

2

2

8

Singhal et al. 2014 [4]

3

2

1

6