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Distribution of reviewed studies by country and year of publication intervals
| Country | Number of studies | |||
|---|---|---|---|---|
| 1990–1999 | 2000–2005 | 2006–2010 | 2011–2018 | |
| United Kingdom | 0 | 1 | 3 | 8 |
| Australia | 0 | 0 | 5 | 13 |
| Ireland | 0 | 0 | 0 | 2 |
| United States | 1 | 4 | 1 | 16 |
| Canada | 0 | 1 | 3 | 6 |
| Sweden | 0 | 0 | 0 | 1 |
| Switzerland | 0 | 0 | 0 | 2 |
| Singapore | 0 | 1 | 0 | 0 |
| Norway | 0 | 0 | 1 | 1 |
| Austria | 0 | 0 | 0 | 1 |
| France | 0 | 0 | 0 | 2 |
| Germany | 0 | 0 | 0 | 1 |
| Portugal | 0 | 0 | 0 | 1 |
| Belgium | 0 | 0 | 1 | 1 |
