Table 10.
Clusters of countries using VOS viewer
| 1991–2000 (T1) | 2001–2010 (T2) | 2011–2021 (T3) | |
|---|---|---|---|
| Countries | 42 | 186 | 253 |
| Countries (threshold = 20 publications) | 21 | 25 | 58 |
| Clusters | 1 | 2 | 5 |
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