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Countries in which studies were conducted
| Country | Number of studies |
| Canada | 13 |
| China | 16 |
| Congo-Kinshasa, Congo-Brazzaville and Uganda | 1 |
| Germany | 1 |
| Japan | 1 |
| Liberia | 2 |
| Saudi Arabia | 5 |
| Sierra Leone | 3 |
| Singapore | 4 |
| South Korea | 6 |
| Spain | 1 |
| Taiwan | 10 |
| The Netherlands | 1 |
| USA | 4 |
| Various | 3 |
