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Table 2 (section: Category†) contained some errors. The correct version of the table is as follows.
Table 2 Summary information about included studies (n=30)
| Studies (n, (%)) | Female football players (n (%)) | Male football players (n (%)) | All football players (n (%)) | |
| Control of type-1 errors | ||||
| Appropriate | 12 (40.0) | 104 (27.4) | 414 (31.6) | 518 (30.6) |
| Inappropriate / unclear | 18 (60.0) | 275 (72.6) | 898 (68.4) | 1173 (69.4) |
| Total | 30 (100.0) | 379 (100.0) | 1312 (100.0) | 1691 (100.0) |
| Selection of controls | ||||
| Appropriate | 12 (40.0) | 12 (11.1) | 224 (54.2) | 236 (45.3) |
| Inappropriate / unclear | 8 (26.7) | 96 (88.9) | 189 (45.8) | 285 (54.7) |
| NA | 10 (33.3) | N/A | N/A | N/A |
| Total | 30 (100.0) | 108 (100.0) | 413 (100.0) | 521 (100.0) |
| Response rate* | ||||
| High (>50%) | 7 (23.3) | 0 (0.0) | 462 (35.2) | 462 (27.3) |
| Low (≤50%) | 3 (10.0) | 0 (0.0) | 135 (10.3) | 135 (8.0) |
| Not reported | 20 (66.7) | 379 (100.0) | 715 (54.5) | 1094 (64.7) |
| Total | 30 (100.0) | 379 (100.0) | 1312 (100.0) | 1691 (100.0) |
| Gender | ||||
| Football players | N/A | 379 (22.4) | 1312 (77.6) | 1691 (100.0) |
| Control subjects | N/A | 108 (20.7) | 413 (79.3) | 521 (100.0) |
| Category† | ||||
| NCT | 23 | 365 | 1153 | 1518 |
| Case-control studies | 1414-16 27-29 31 34 37 38 47 52 57 59 | 56 | 525 | 581 |
| Impact of heading | 1712-19 28 29 32 34 37 52 53 57 59 | 310 | 863 | 1173 |
| Impact of head-injuries | 1313-19 27 31-33 49 52 | 293 | 810 | 1103 |
| Neuroimaging | 817 37 38 44 48 50 51 54 | 22 | 121 | 143 |
| EEG | 255 56 | 0 | 106 | 106 |
| Postural control | 137 | 0 | 15 | 15 |
| Level of play‡ | ||||
| Youth | 3 (10.0) | 69 (18.2) | 100 (7.6) | 169 (10.0) |
| High-school / college | 9 (30.0) | 280 (73.9) | 234 (17.8) | 514 (30.4) |
| University | 3 (10.0) | 22 (5.8) | 47 (3.6) | 69 (4.1) |
| Amateur | 2 (6.7) | 8 (2.1) | 62 (4.7) | 70 (4.1) |
| Professional | 8 (26.7) | 0 (0.0) | 677 (51.6) | 677 (40.0) |
| Former professional | 5 (16.7) | 0 (0.0) | 192 (14.6) | 192 (11.4) |
| Total | 30 (100.0) | 379 (100.0) | 1312 (100.0) | 1691 (100.0) |
*Fraction of participants that agreed to participate after being invited to participate in the study. This includes football players and control participants.
†Some studies provided testing for more than one modality (eg, neurocognitive testing and neuroimaging or neuroimaging and balance testing), resulting in a total study number larger than 31. Within neurocognitive testing, also some studies provided case–control data as well as a correlation analysis for, for example, heading frequency and neurocognitive deficits in the football players.
‡Level of play as reported in the original studies. Age range for youth football players was 10–131 and 13–18.2 The category ‘High school/college’ includes the ‘interscholastic’ as well.
NA, not available; NCT, neurocognitive testing.