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Study locations.
| Country | Statistics, n (%) |
| United States | 48 (76.2) |
| Germany | 5 (7.9) |
| United Kingdom | 3 (4.8) |
| China | 3 (4.8) |
| The Netherlands | 3 (4.8) |
| Australia | 1 (1.6) |
| Canada | 1 (1.6) |
| Total | 64a |
aOne study was conducted in both China and the United States.
