Table 3.
Continents of included studies.
| Continent | Number of studies |
|---|---|
| Europe | 29 |
|
| |
| Asia | 23 |
|
| |
| North America | 19 |
|
| |
| Australia and New Zealand | 8 |
|
| |
| Africa | 0 |
|
| |
| Central and South America | 0 |
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