| Dominant variable | Africa | Asia | Latin America | Europe | Total |
| Human | 10 | 3 | 1 | 1 | 15 |
| Natural | 8 | 7 | 1 | 0 | 16 |
| Combined | 7 | 1 | 0 | 0 | 8 |
| Total | 25 | 11 | 2 | 1 | 39 |