Study

Reporting

(0-13)

External validity

(0-3)

Bias

(0-6)

Confounding

(0-5)

Power

(0-1)

Total

(0-28)

Lew (1990)

8

0

4

1

0

13

Faerovig and Zachrisson (1999)

9

0

4

1

0

14

Ning et al. (2009)

9

1

3

1

0

14

Ning and Duan (2010)

9

1

3

1

0

14

Kuroda et al. (2010)

9

0

5

1

0

15

He et al. (2013)

10

1

5

3

0

19

Janson et al. (2014)

9

0

5

1

0

15

Yu et al. (2016)

11

1

4

1

1

18

Nakamura et al. (2017)

11

1

4

4

1

21