Quality assessment of included studies based on Newcastle-Ottawa Scale checklist
| Study [ref.] | Selection (maximum of 4 stars) | Comparability (maximum of 2 stars) | Outcome assessment (maximum of 3 stars) |
| Lang [12] | *** | ** | ** |
| Sasaki [11] | *** | ** | |
| Borrell [14] | *** | ** | ** |
| Lang [15] | *** | ** | ** |
| Schatz [19] | *** | *** | |
| Sah [24] | *** | *** | |
| Quinto [20] | **** | ** | *** |
| Lang [16] | **** | ** | ** |
| Kattan [17] | **** | ** | * |
| Hom [21] | **** | * | |
| Vargas [22] | *** | * | |
| Luder [23] | *** | *** |
In this checklist, the highest quality studies are awarded up to 9 stars.