Country group | Year | ||||
1997 n% (95% CI) | 2002 n% (95% CI) | 2007 n% (95% CI) | 2012 n% (95% CI) | 2017 n% (95% CI) | |
USA | 204 68.2 (62.6 to 73.4) | 190 59.6 (53.9 to 65.0) | 177 44.7 (39.8 to 49.8) | 262 41.3 (37.4 to 45.2) | 231 35.3 (31.7 to 39.1) |
UK | 51 17.1 (13.1 to 21.9) | 50 15.7 (12.0 to 20.2) | 62 15.7 (12.3 to 19.7) | 67 10.5 (8.3 to 13.3) | 37 5.7 (4.1 to 7.8) |
Australasia | 17 5.7 (3.5 to 9.1) | 29 9.1 (6.3 to 12.9) | 60 15.1 (11.8 to 19.2) | 77 12.1 (9.7 to 15.0) | 81 12.4 (10.0 to 15.2) |
Europe | 11 3.7 (2.0 to 6.7) | 24 7.5 (5.0 to 11.1) | 40 10.1 (7.40 to 13.6) | 70 11.0 (8.8 to 13.9) | 135 20.6 (17.6 to 24.0) |
Canada | 7 2.3 (1.0 to 5.0) | 12 3.7 (2.1 to 6.7) | 10 2.5 (1.3 to 4.8) | 27 4.3 (2.9 to 6.2) | 25 3.8 (2.5 to 5.7) |
Other* | 9 3.0 (1.5 to 5.8) | 14 4.4 (2.5 to 7.4) | 47 11.9 (8.9 to 15.6) | 132 20.8 (17.7 to 24.2) | 145 22.2 (19.1 to 25.6) |
Total | 299 (100%) | 319 (100%) | 396 (100%) | 635 (100%) | 654 (100%) |
*See online supplementary appendix 2 for other country details.