Number of articles with at least N affiliation countries/regions
| Time Span | n = 2 | n = 3 | n = 4 | n = 5 | n = 6 | n = 7 | n = 8 | n = 9 | n = 10 |
|---|---|---|---|---|---|---|---|---|---|
| All | 1456 | 250 | 74 | 36 | 21 | 8 | 4 | 2 | 2 |
| 1980–1989 | 72 | 5 | 1 | 0 | 0 | 0 | 0 | 0 | 0 |
| 1990–1999 | 183 | 12 | 1 | 0 | 0 | 0 | 0 | 0 | 0 |
| 2000–2009 | 453 | 65 | 12 | 6 | 4 | 0 | 0 | 0 | 0 |
| 2010–2018 | 748 | 168 | 60 | 30 | 17 | 8 | 4 | 2 | 2 |