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Top 10 countries in terms of the number of studies published in 2002–2021.
| No. | Country | Counts | Centrality | No. | Country | Counts | Centrality |
| 1 | China | 139 | 0 | 6 | South Korea | 38 | 0 |
| 2 | The USA | 98 | 0.38 | 7 | The UK* | 36 | 0.33 |
| 3 | Italy | 63 | 0 | 8 | Spain | 22 | 0.08 |
| 4 | Turkey | 59 | 0 | 9 | Brazil | 20 | 0 |
| 5 | Germany | 44 | 0.13 | 10 | France | 20 | 0.11 |
*The UK including England, Scotland, Wales, and Northern Ireland.
