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Number of studies per country.
| Country | Number of studies |
|---|---|
| USA | 62 |
| UK | 12 |
| Sweden | 7 |
| Italy | 5 |
| Canada | 4 |
| China | 2 |
| Japan | 2 |
| Australia | 1 |
| Austria | 1 |
| Belgium | 1 |
| Denmark | 1 |
| Finland | 1 |
| Germany | 1 |
| Netherlands | 1 |
| Norway | 1 |
| Poland | 1 |
| South Korea | 1 |
| Denmark/Norway | 1 |
| UK/Germany/Netherlands | 1 |
| USA/Netherlands | 1 |
|
| |
| Total of studies | 107 |
