Table 2 Quality assessment according to the Newcastle–Ottawa scale

Kim 2015 [3]

3

2

3

8

Zhong 2020 [4]

4

2

2

8

Nomori 2018 [5]

4

2

3

9

Takizawa 1999 [6]

4

2

3

9

Tane 2019 [7]

4

2

3

9

Helminen 2020 [1]

3

2

2

7

Gu 2018 [8]

4

2

3

9

Kobayashi 2017 [9]

4

2

3

9

Keenan 2004 [10]

2

1

3

6

Kashiwabara 2009 [11]

4

2

3

9

Macke 2015 [12]

4

2

3

9

Saito 2014 [13]

4

1

3

8

Yoshimoto 2010 [14]

3

2

2

7

Hwang 2015 [15]

4

2

2

8