Table 2.
Total score on the risk of bias assessment.
| Studya | Total score (out of 28) | Category |
| Alemanno et al [62] | 22 | Good |
| Amin et al [44] | 19 | Fair |
| Botella et al [55] | 16 | Fair |
| Brown et al [63] | 24 | Good |
| Chau et al [73] | 16 | Fair |
| Collado-Mateo et al [56] | 24 | Good |
| Darnall et al [81] | 25 | Good |
| Fowler et al [45] | 21 | Good |
| Garcia-Palacios et al [57] | 23 | Good |
| Garrett et al [46] | 18 | Fair |
| Griffin et al [80] | 20 | Good |
| Gromala et al [47] | 18 | Fair |
| Guarino et al [48] | 10 | Poor |
| Harvie et al [68] | 20 | Good |
| Herrero et al [58] | 18 | Fair |
| House et al [82] | 19 | Fair |
| Jin et al [49] | 18 | Fair |
| Jones et al [50] | 16 | Fair |
| Matamala-Gomez et al [74] | 19 | Fair |
| Matheve et al [64] | 24 | Good |
| Monteiro et al [65] | 21 | Good |
| Mortensen et al [59] | 18 | Fair |
| Mouraux et al [76] | 14 | Poor |
| Ortiz-Catalan et al [77] | 18 | Fair |
| Pamment and Aspell [51] | 20 | Good |
| Phoon Nguyen et al [83] | 21 | Good |
| Rezaei et al [69] | 25 | Good |
| Rutledge et al [78] | 18 | Fair |
| Sarig-Bahat et al [70] | 23 | Good |
| Sarig-Bahat et al [71] | 21 | Good |
| Sato et al [75] | 12 | Poor |
| Shahrbanian et al [52] | 17 | Fair |
| Solca et al [84] | 19 | Fair |
| Tejera et al [72] | 23 | Good |
| Thomas et al [66] | 25 | Good |
| Tong et al [79] | 16 | Fair |
| Trujillo et al [67] | 17 | Fair |
| Villafaina et al [60] | 23 | Good |
| Villafaina et al [61] | 22 | Good |
| Wiederhold et al [53] | 11 | Poor |
| Wiederhold et al [54] | 8 | Poor |
aEach study was scored on all 27 items of the modified Downs and Black checklist. On the basis of the total score, all included studies were categorized as presenting poor, fair, good, or excellent quality. A total score of ≤14 out of 28 was considered poor quality, 15-19 was considered fair, 20-25 was considered good, and 26-28 was considered excellent methodological quality.