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Newcastle-Ottawa scoring system for nonrandomized comparative studies
| Ref. | Selection star | Comparability star1 | Outcome star | Total star |
| Osugi et al[9] | 3 | 2 | 3 | 8 |
| Shinoto et al[10] | 3 | 2 | 3 | 8 |
| Nunobe et al[13] | 4 | 2 | 3 | 9 |
| Fukuhara et al[14] | 3 | 2 | 3 | 8 |
| Kojima et al[21] | 3 | 2 | 3 | 8 |
| Namikawa et al[22] | 3 | 2 | 2 | 7 |
| Tanaka et al[23] | 3 | 2 | 3 | 8 |
| Kumagai et al[24] | 3 | 2 | 1 | 6 |
| Kim et al[25] | 3 | 2 | 2 | 7 |
Factors considered: Age, gender; American Society of Anesthesiologists grading and tumor stage.
